WO2001075359A1

WO2001075359A1 - High power led source and optical delivery system

Info

Publication number: WO2001075359A1
Application number: PCT/US2001/004580
Authority: WO
Inventors: Thomas J. Brukilacchio
Original assignee: Getinge/Castle, Inc.
Priority date: 2000-04-03
Filing date: 2001-02-13
Publication date: 2001-10-11

Abstract

A high optical power light source has an LED (152) arranged to emit light through an exit surface, a transparent window (154) secured to this surface and a hemispherical lens (160) on the opposed side of the window from the exit surface, this hemispherical lens being centered on the light-emitting diodes. In a preferred embodiment, the LED is formed as a single, continuous semi-conductor device provided on both sides with patterned conductors which define at least one pair of electrodes, so that when a potential difference is applied across these pairs, the current flow through the substrate causes emission of light from multiple areas of the substrate, substantially perpendicular thereto, thus causing the substrate to act as an LED. The light from this source can be focused by an auxiliary lens system (162) into an optic fiber (164) with very high coupling efficiency.

Description

TITLE: HIGH POWER LED SOURCE AND OPTICAL DELIVERY SYSTEM

BACKGROUND OF THE INVENTION

This invention generally relates to a light source especially, though not exclusively, intended for use in surgical lighting in operating rooms and ambulatory surgical suites. This invention also relates to a light emitting diode (LED) array which is used in this light source but which may also be useful in other types of optical systems and applications.

For decades, illumination systems for operating rooms have posed major problems. To ensure the safety of patients, it is essential that an illumination system provide intense and acceptably uniform illumination over the entire surgical site, which can in some cases, be of substantial width and depth as, for example in open heart surgery. Obviously, the surgery cannot be interrupted should a bulb burn out, and thus each lighting unit needs either multiple bulbs or at least a back-up bulb which will illuminate should a primary bulb fail. Also, large area systems need at least two, and preferably three or more, lighting units to ensure that light can impinge upon the surgical site from multiple directions so that no part of the surgical site is in complete shadow even when it is necessary for operating room personnel to be positioned between the surgical site and one of the lighting units. The lighting units must also be suspended so that they can be moved and rotated in all directions to provide optimum illumination of the surgical site, the size and shape of which may change during a surgical procedure

Lighting units containing multiple high output bulbs sufficiently powerful to produce the intense lighting needed for surgery or to meet code redundancy requirements are necessaπly of substantial depth and weight To enable such large heavy lighting units to be moved by operating room personnel without requiπng undue force, it is essential in practice to provide some form of counterpoise system, and the presence of the counterpoise system further increases the size and weight of the lighting units Conventional surgical lighting systems have other disadvantages The powerful lamps used, which each typically compπse a bulb and a reflector, generate large amounts of heat and infra-red radiation The heat is dissipated into the operating room, thus increasing the load on associated heating, ventilating and air conditioning (HNAC) systems, and is also radiated on to operating room personnel, increasing their fatigue duπng lengthy procedures Since the infra-red radiation generated follows the same path as the visible light, it is thus largely absorbed at the surgical site, withm the patient's tissues This radiation absorption by the patient's tissues tends to damage the tissues, especially duπng lengthy procedures, and generally increases the trauma to the patient resulting from the operation It is also essential that the illumination produced by the system conform to a standard of color to ensure that tissues, blood, blood vessels, and the like, all retain their normal appearance, since any deviation from expected colors of body parts increases the πsk of a surgeon mistakenly identifying a body part and thus operating mcoπectly In practice, a surgical illumination system must produce light with a proper correlated color temperature ("CCT", which is defined as the absolute temperature of a black body whose chromaticity most nearly resembles that of the light source) and a proper color rendeπng index ("CRI", which is defined as the average color shift, under illumination by a test source, of a seπes of eight standard colors of intermediate saturation spread throughout the range of hues, with respect to a reference source) The need to maintain accurate CCT and CRI values presents problems when it is necessary to control the output of surgical lighting systems. Conventionally, light intensity has been controlled by varying the energy input to each lamp. However, all types of high output lamps undergo some change in their output spectrum as their energy input is varied, thus changing the CCT and CRI of the output. In practice, this tends to result in an unsatisfactory compromise since the usable intensity range is reduced and the resultant changes in CCT and CRI, though tolerable, are greater than is strictly desirable.

Attempts have been made to avoid the aforementioned longstanding disadvantages of conventional surgical lighting systems using lamps carried within lighting heads disposed inside the operating room. In particular, inventors have realized that fiber optic technology, which permits light from a remote source to be channeled through a bundle of optical fibers to a location where the light is needed, allows the development of surgical lighting systems in which the actual light sources may be outside the operating room and the light is fed to the surgical site via optical fiber bundles. Such a fiber optic based system renders the light sources accessible to technicians should a light source fail during an operation, and eases the problem of maintaining the lighting heads aseptic, since the lighting heads no longer need to contain bulbs and reflectors of complex shape. Also, the lighting heads themselves could be made smaller and lighter, thus avoiding the need for elaborate counterpoising systems. Finally, the removal of the light sources from the operating room also removes the unwanted heat generated within the operating room by conventional lighting systems.

Most proposals for use of fiber optic based lighting systems within operating rooms relate to so-called "surgical headlamps", that is to say, lighting systems which provide light adjacent a surgeon's face for illumination of a surgical site very close to the face, as required in microsurgery, for example, eye or ear surgery. Examples of such surgical headlamp systems are described in U.S. Patents Nos. 4,516,190; 5,355,285; 5,430,620; and 5,709,459. However, at least one fiber optic based system has been proposed to replace the main conventional lighting system of an operating room, see U S Patent No 5,497,295 (Gehly), Figures 5 et seq In the Gehly system, the light sources are disposed withm a separate room outside the operating room Light from these sources is led via a plurality of optic fiber bundles (one bundle for each lighting head used withm the operating room) into the operating room via a central hub installed in the ceiling thereof Beneath this central hub are mounted two substantially cylmdπcal rotatable members having a common vertical axis Each of the rotatable members carπes a honzontal arm which extends outwardly from the rotatable member parallel to the ceiling of the operating room A carnage is shdably mounted on each honzontal arm so as to be movable along the length of the arm, and each carnage supports a three-segment telescopic vertical column which descends from the carriage A shallow, dish-shaped hghthead is mounted via a flexible coupling on the bottom of each telescopic column Each of the fiber bundles enteπng the operating room via the central hub is led via one of the cyhndπcal rotatable members on to one of the honzontal arms (each arm carπes only one fiber bundle) and down the associated column and flexible coupling to the center of the associated hghthead, where the light impinges upon a substantially conical central section of the hghthead, which deflects it on to a plurality of annular reflectors which surround the conical central section

The honzontal arm/carπage/telescopic column/flexible coupling/ hght- head structure descπbed m Gehly is of considerable complexity, size and weight, so that the arms, carnages and columns appear to require powered operation (with inevitable problems should any part of the complex mechanical structure fail to operate coπectly dunng the course of a surgical procedure), and the whole structure is probably as intrusive in an operating room as conventional lighting heads containing bulbs Furthermore, the fiber bundles in Gehly extend unbroken from adjacent the light sources to the hghtheads, with no apparent provision for relieving stress on the bundles caused by relative movements between the vaπous parts of the supporting structure Thus, it would appear that the apparatus does not permit completely free rotation of the arms nor more than a limited range of motion of the hghtheads, and even then, wear upon, or damage to the bundles, may be expected after repeated relative movements between the various parts of the supporting structure.

The '689 application describes an illumination system, adapted for surgical lighting, which, like the Gehly system, enables the light sources to be placed remotely from an operating room, thereby reducing the bulk of the lighting heads required within the room. However, the '689 illumination system enables light to be transmitted from the remote sources to the lighting heads using a simpler, less bulky structure which does not require powered operation (though such operation is not excluded), and can provide means for real time control of lighting intensity and CRI. The '689 application also describes an illumination system which enables light from a plurality of sources to be mixed to provide uniform lighting having a desired CCT and/or CRI, and which enables light from a plurality of sources to be mixed to provide uniform lighting having a desired CRI and/or CCT, and which provides for feedback to ensure compliance with CRI or other color standard requirements. The '689 system also provides a fiber based illumination system having at least one termination to a surgical light head which allows for the connection of one or more endoscope illumination or surgical headlamp fiber optic bundles or light guides.

The '689 system achieves these advantages by providing two light sources having different spectral distributions, and mixing the light from these two sources in varying proportions to provide light having a desired CCT and/or CRI. In the preferred forms of the system illustrated in the '689 application, the two light sources are an incandescent source, preferably using metal halide lamps, and an LED array, which provides red-biased light. The specific LED anay shown in Figures 6 and 7 of the '689 application is of a generally conventional type, in which a large number of discrete LED's are formed into a close-packed array such that the output surfaces of the LED's lie in a single plane, and a focusing lens focuses the light from the array into a fiber optic bundle.

This type of LED anay is certainly capable of producing red-biased light of the intensity (about 5 Watts optical delivered into the aperture of the fiber optic bundle) required by the '689 system. However, this type of LED anay does have a number of practical disadvantages. The accurate assembly of the 400 or so individual LED's required into the desired planar anay, and the connection of the two conductors from each LED, are tedious, time-consuming and must be conducted manually since they are extremely difficult to automate. Furthermore, it is burdensome to assure accurate alignment of the LED's and formation of a planar anay. Finally, because of the large size of the array, it is difficult to couple the full output of the anay efficiently into the fiber optic bundle; not only is such inefficient coupling wasteful of energy (the electrical power consumption of the LED is about 150 W) but, because it increases the light output needed from the anay, it exacerbates the already-difficult problem of cooling the anay, which itself requires additional electrical power.

Accordingly, it is an object of the present invention to provide an LED anay which can be substituted for that described in the '689 application and which provides more efficient coupling of the LED output into a fiber optic bundle. It is also an object of the present invention to provide an LED anay with a large numerical aperture.

It is a further object of the present invention to provide an LED anay which does not require accurate manual alignment of a large number of individual LEDs or connection of separate conductors to each LED. It is a further object of the present invention to provide an LED anay which allows efficient cooling of the anay.

It is a further object of the invention to provide an LED anay comprising a large number of LED's and which can readily and economical be fabricated by techniques well-known to those skilled in contemporary semiconductor technology.

It is another object of the present invention to provide a high power LED source that makes efficient use of electrical power.

It is yet another object of the present invention to provide an optical coupling out system for use with a high power LED source to make more efficient use of available optical power than would otherwise be possible absent the optical system. Other objects of the invention will in part appear hereinafter and will in part be obvious when the following detailed descπption is read m connection with the drawings

SUMMARY OF THE INVENTION In one aspect, this invention provides a light source compnsmg an LED ananged to emit light through an exit surface, a transparent window secured to the exit surface, and a lens having substantially the form of part of a sphere, this part- sphencal lens being disposed on the opposed side of the window from the LED anay, and the center of curvature of this lens being disposed on or adjacent the LED anay

This invention also compnses a high optical power LED comprising a semi-conductor substrate having first and second surfaces on opposed sides thereof and also having light-emission characteπstics such that flow of cunent from the first to the second surface of the substrate will cause light to be emitted from the substrate emitting surface This LED further compnses at least on pair of electrodes, one of each pair being disposed on the first and the other on the second surface of the substrate, whereby application of a potential difference between the electrodes of each pair causes flow of cunent through the substrate and emission of light from discrete areas of the substrate lying between each of the at least one pair of electrodes, thereby causing the substrate to act as a plurality of hght-emittmg diodes and emit light from its first surface

Other features include an efficient cooling system and an imaging optical system for efficient coupling of optical power from the array into the aperture of a bundle of distant optical fibers Other advantages and features will become apparent from the following descπption and claims

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation, and methodology of the invention, together with other objects and advantages thereof, may best be understood by reading the detailed descπption in connection with the drawings in which unique reference numerals have been used throughout for each part or feature and wherein

Fig 1 is a block diagram showing schematically the major components and subsystems of an illumination system of the present invention used for surgical lighting,

Fig 2 is a diagrammatic perspective view of the components of the illumination system shown m Fig 1 as they appear mside an operating room,

Fig 3 is a three quarter view of the halide lamp assembly shown in Fig 1 from m front and to one side, Fig 4 is a diagrammatic section through one of the lamps and its associated coupling cell shown in Fig 3,

Fig 5 is a diagrammatic section similar to Fig 4 but showing an alternate type of coupling cell,

Fig 6 is a partially exploded perspective view of the light emitting diode assembly shown in Fig 1 ,

Fig 7 is a side elevation view of the LED assembly shown m Fig 6, together with its associated fiber optic bundle, and shows the paths of selected rays traveling from the LEDs to the fiber optic bundle via an intervening imaging system,

Fig 8 is an enlarged three-quarter perspective view, from in front and to one side, of part of the LED assembly shown in Fig 6 as actually assembled,

Fig 9 is an enlarged three-quarter perspective view, from in front and to one side, of the LED anay shown in Figs 6, 7, and 8 showing individual emitting areas thereof,

Figs 10 and 11 are diagrammatic top plan views of alternative LED anays which may be substituted for that shown in Fig 9,

Fig 12 shows diagrammatically the components of the light mixer/feedback module and vaπable aperture/shutter module shown in Fig 1 ,

Fig 13 shows diagrammatically an alternative anangement of hght mixer/ feedback module and variable aperture/shutter module which can be substituted for that shown in Fig 12, Fig 14 is a cross-section taken along line B-B of Fig 13, Fig 15 is a diagrammatic perspective of an alternative termination to a surgical lighting head of the invention which allows for the connection of one or more surgical head lamps that receive illumination via fiber optic bundles or light guides, and

Fig 16 is a diagrammatic perspective of an alternative termination to a surgical light head of the invention which allows for the connection of one or more endoscopes that receive illumination via fiber optic bundles or light guides

DETAILED DESCRIPTION OF THE INVENTION The accompanying drawings illustrate an illumination system including a light source of the present invention This illumination system is used for surgical lighting, but can readily be adapted for other applications in which intense illumination and accurate color rendition are required over a substantial work area or volume For fuller details of the components of the illumination system other than the light sources and anangements for mixing light from these sources, the reader is refened to the aforementioned '689 application

As shown in Fig 1 , the illumination system (generally designated 10) is divided into three mam sections, namely a remote section (indicated by the broken rectangle 12), which is preferably located withm a lamp housing located withm an operating room in an easily accessible wall recess or may be installed in a non-aseptic room adjacent, but separate from, the operating room so that it can be accessed by technicians while a surgical procedure is m progress, a canopy section (indicated by the broken rectangle 14), which is installed m a canopy located directly above the ceiling of the operating room, and an operating room section (indicated by the broken rectangle 16), which is installed within the operating room itself Neither the division of the illumination system 10 among the three sections 12, 14 and 16, nor the allocation of particular components and sub-systems to any one of these three sections is essential to the present invention, as will be apparent from the detailed descπption below Numerous changes to this division and allocation can be made without departing from the scope of the invention. For example, the canopy section could be eliminated entirely, and the components thereof removed to the remote section. Also, the illumination system per se is not restricted to the use of an incandescent source and a light emitting diode source, but could, for example, be practiced with two light emitting diode sources, lasers, or laser diodes (LDs), having different spectral characteristics (provided, of course, that adequate attention was paid to the safety regulations governing high powered LED and laser and LD sources).

The remote section 12 comprises a lamp assembly 18 containing several metal halide lamps, and a fan 20 which is used to cool the lamp assembly 18. The remote section 12 also comprises a control module 22, which controls the output from the lamp assembly 18 in a manner to be described below, a power supply 24, which supplies power to both the lamp assembly 18 and the control module 22 via lines 26 and 28, respectively, and a status indicator 30, which serves to advise technicians of the status of various components of the system 10. Since operating room personnel may also desire to know the status of the system 10, it may alternatively be desirable to locate the status indicator 30 within the operating room section 16, or at least to duplicate information from the status indicator 30 within the operating room section 16.

The output from the lamp assembly 18 is fed via a "halide" fiber opti bundle 32 to a light mixer/feedback module 34 located within the canopy section 14. The light mixer/feedback module 34 also receives the output from a light emitting diode (LED) assembly 36 via an "LED" fiber optic bundle 38. The LED assembly 36 receives power from the power supply 24 via a line 40, and is controlled by control module 22, as indicated by line 42. The output from the light mixer/feedback module 34 is fed to a variable aperture/shutter module 44 and thence via a fiber optic bundle 46 to a light splitter 48 located within the operating room section 16. The light splitter 48 divides the output from the bundle 46 among three separate fiber optic bundles 50A, 50B and 50C, which pass through separate light pipe/joint assemblies 52 to three separate lighting heads 54. The three lighting heads 54 direct separate beams on to a target area 56 disposed within the operating room. As will be seen later, one of the lighting heads may be replaced by a fiber cable connector port to feed color controlled light to fiber bundles leading to surgical headlamps and/or endoscopes.

The physical form of the various components of the operating room section 16 shown in Fig. 1 may be seen in Figure 2, which shows a diagrammatic perspective view of the operating room section 16. (For ease of illustration, and to avoid crowding of the drawing, one of the three lighting heads 54 and its associated light pipes and joints are omitted from Fig. 2). As shown in Fig. 2, the operating room section 16 comprises a vertical cylindrical hub 70, which is mounted on the ceiling of the operating room. Vertical cylindrical sections 72 and 74 are mounted beneath and coaxial with the hub 70, each of these cylindrical sections 72 and 74 carrying a horizontal arm 76 or 78, respectively. The sections 72 and 74 can rotate freely relative to each other and to the hub 70, so that the arms 76 and 78 can extend horizontally in any desired direction from the hub 70. Although not visible in Figure 2, the light splitter 48 is housed within the hub 70 and sections 72 and 74. The single fiber optic bundle 46 (Fig. 1) canies light from the canopy section 14 through the ceiling of the operating room into the hub 70, where the light splitter 48 (Fig. 1) divides this light between separate fiber optic bundles (not shown in Fig. 2) running within the horizontal arms 76 and 78. Since the structures attached to arms 76 and 78 are identical, only that attached to arm 76 will hereinafter be described in detail. The horizontal arm 76 is connected via a fixed (non-articulated) elbow 80 to a vertical section 82, which is coaxial with a lower vertical section 84. The lower section 84 can rotate freely relative to the upper section 82, and is connected via a preferably counterpoised, articulating joint 86 to a "horizontal" arm 88 (obviously, the arm 88 may be inclined away from the horizontal depending upon the position of the joint 86). The cross-sections of vertical section 84 and arm 88 are enlarged adjacent joint 86. The arm 88 is coaxial with a further horizontal arm 90 and may be connected thereto by a joint 92, which is a fully rotatable fiber joint of the present invention and which permits free rotation between the arms 88 and 90. The outer end of the arm 90 is connected to an arcuate tube 94, which supports a lighting head 54. As most easily seen on the left hand side of Fig 2, the arcuate tube 94 is actually connected to a tube 96, which extends radially inwardly into, and supports, the lighting head 54.

Light entering the fiber optic bundle lying within the horizontal arm 76 passes via the bundle to the joint between the vertical sections 82 and 84, where it enters a second fiber optic bundle which extends through the section 84, the joint 86, the arms 88 and 90, the arcuate tube 94 and the radial tube 96, finally emerging into the lighting head 54, where it is directed on to the target area 56 (Figs. 1 and 2). The free rotation of the arm 76 relative to the hub 70, together with the free rotation between the vertical sections 82 and 84 and that of the joint 92, and the ability of the lighting head 54 to pivot about the radial tube 96, give the lighting head 54 complete freedom of movement. Furthermore, the operating room section of the illumination system is sufficiently light in weight so that it can readily be manipulated manually by operating room personnel, no power operation being required. Before a detailed description of the various components of the remote and canopy sections, 12 and 14, is given, it is believed desirable to explain the design philosophy behind the light generating system of the present illumination system. As already discussed, a surgical illumination system must produce light with a proper CCT and a proper CRI. Although metal halide lamps, such as those used in the lamp assembly 18 (Fig. 1) are efficient light sources, their output is biased towards the blue end of the visible spectrum. Furthermore, the already inadequate red light intensity provided by these metal halide lamps is further diminished as the light passes through the various fiber optic bundles and light pipes used in the present apparatus, since these bundles and light pipes are formed of plastic materials which tend to selectively absorb red light. Accordingly, it is necessary to mix the light from the metal halide lamps with light which is biased towards the red end of the visible spectrum, and in the present apparatus, such red-biased light is provided by the LED assembly 36. The apparatus must blend these two light sources to produce a completely homogeneous output, since even slight variations in color or intensity of illumination within the target area (i.e., the operating site) are unacceptable in a surgical lighting system. Furthermore, since the spectral output from lamps may vary as the lamps age, the illumination system desirably provides some means by which the actual light output can be sampled and the proportions of light from the two sources used can be vaned to provide a final light output accurately conforming to the desired CCT and CRI Finally, the illumination system desirably allows the intensity of illumination of the target areas to be varied substantially (since, for example, more light may be required for a surgical procedure earned out deep withm a body cavity than for one earned out on the surface of the skin) without significant change in the CCT and CRI of the light Such variation in light intensity should be achievable without changing the power input to the metal halide lamps in the lamp assembly 18, since varying the power input to metal halide lamps results in substantial changes in the spectral characteπstics of the light output therefrom

In the present illumination system, the foregoing objectives are achieved m the following ways Light from each of the lamps within the lamp assembly 18 is passed through a variable aperture and then into the input end of fiber optic bundle 32 (See Fig 1) Similarly, light from the LED assembly 36 is introduced into the input end of bundle 38 Withm the light mixer/feedback module 34, the output ends of the fibers of the two bundles 36 and 38 may be randomly intermingled as needed to form a single fiber optic bundle, the output from which is essentially the sum of the inputs to the two bundles The light exiting the combined bundle is received into an optical homogenizer, m the form of a multimode light pipe, which mixes the light to ensure that a truly homogeneous light flux is produced The resultant light flux is sampled to determine if it has the conect CCT and CRI, and if not, the light mixer/feedback module 34 sends a signal to the control module 22 to adjust the LED assembly 36 to vary the proportion of light from this light assembly used to produce the final light flux (Such real-time feedback and control of the lamp assembly 18 is stnctly an optional feature of the present apparatus, and may not be needed m many cases, in practice, depending upon what vanations m CCT and CRI are permissible, the stability of the outputs from the halide lamps and the LED assembly used may be sufficient to permit the system to run "open loop", I e , the mixed output from the light mixer/feedback module 34 may be sampled once, and the system adjusted to its optimum output and thereafter left to run for many hours until a recalibration of the output is deemed desirable, for example, when it is necessary to replace a burned-out lamp.) Finally, the intensity of the mixed light leaving the light mixer/feedback module 34 is adjusted by the variable aperture/shutter 44, and the light is then passed to the operating room section 16. Alternatively, sources other than LEDs can be used. For example and without limitation, laser diodes may be used with or instead of LEDs. Fig. 3 shows a three quarter view of the lamp assembly 18. As shown in Fig. 3, the lamp assembly 18 comprises six separate metal halide arc lamps (generally designated 110) ananged in a single vertical column, each lamp 110 comprising a bulb 112 and an associated reflector 114. Each reflector 114 is electroformed and provided with a high efficiency dichroic coating which largely rejects (i.e., does not reflect) both ultraviolet and infrared radiation emitted by its associated bulb 112. Each reflector 114 is substantially part ellipsoidal, being shaped to optimize coupling of the light from the associated bulb 112 into a fiber optic bundle 116, formed from a plastic, a separate bundle 116 being provided for each lamp 110. The input end of each bundle 116 is held within a coupling cell 118, which serves to limit heat generated within the bundle by absorption of the radiation from the bulb 112 and to dissipate the heat generated sufficiently quickly to prevent damage to the plastic fibers within the bundle. The coupling cells 118 are provided with cooling fins 120 and the fan 20 (see Fig. 1 - the fan is not visible in Fig. 3) is disposed within a hollow base portion 122 of the lamp assembly 18 and blows air vertically upwardly over the cooling fins to assist in the dissipation of heat from the coupling cells 118. To direct the air flow from the fan 20 over the coupling cells 118, the lamp assembly 18 is provided with side plates 124 and 126, a rear plate 128 and a front plate (removed from the lamp assembly in Fig. 3 to show the interior details of this assembly). Together these four plates define an elongated rectangular channel within which are disposed the coupling cells 118.

The bulbs 112 are pre-aligned to slide directly into their associated reflectors 114 and maintain the focus position at which the bulb 112 most efficiently couples to its associated bundle 116 If desired, each lamp reflector 114 may be equipped with cooling fins to dissipate heat and thus increase lamp life

The metal halide lamps 110 and the bundles 116 used in the lamp assembly 18 may be readily available commercial units For example, the lamps 110 can be 3200 lumen Welch Allyn 50 Watt halide lamps (available from Welch Allyn, Lighting Equipment, Skaneateleles, NY or Osram VIP270 metal halide lamps (available from Osram Sylvama, Danvers, MA), while the bundles 116 are conveniently Toray Acrylic Fiber Bundle (available from Toray, Japan)

The six separate bundles 116 leaving the coupling cells 118 are combined into the single bundle 32 shown in Fig 1 , which is protected from mechanical damage by a plastic conduit 130 as the bundle 32 runs the substantial distance (typically about 30 feet, approximately 9 meters) from the lamp assembly 18 to the light mixer/feedback module 34 (Fig 1) within the canopy section 14 of the illumination system This distance may vary depending on the separation architecture between the mixer/feedback module 34 and the lighting assemblies

Fig 4 is an enlarged view, mostly in section, showing the details of one of the lamps 110 shown in Fig 3 and its coupling cell 118 and associated apparatus It will be seen from Fig 4 that a vaπable aperture 132 may be disposed between the side plate 124 and the coupling cell 118 Such a vanable aperture 132 is controlled by the control module 22 (Fig 1) and serves to regulate the amount of light from the lamp 110 entering the coupling cell 118, thereby varying the proportion of light from the lamps 110 m the final mixed light output in the manner already descnbed The vaπable aperture 132 may also, of course, be used, inter aha, to compensate for changes in the brightness of the lamp 110 as the lamp ages Alternatively, this function may be accomplished electronically

The coupling cell 118 compnses a sapphire window 134 which allows light to enter the cell 118, and which is fixed in position withm an axial bore formed withm the hollow metallic cyhndncal body 136 of the cell 118 Sapphire is used to form the window 134 because of its high transmission from the UN through the mid-IR region of the spectrum and its high thermal conductivity It is preferably provided with a dielectric coating that is highly reflective of ultraviolet and infrared radiation from the lamp 110, and thus limits the amounts of unwanted non-visible radiation enteπng the cell 118 Having high thermal conductivity, sapphire operates to dissipate heat For this purpose, good thermal contact between the sapphire window 134 and the body 136 is ensured by having the edge of the window 134 metallized and then soldered (the soldenng is not shown in Fig 4) to the body 136 or affixed with conductive silica epoxy

As shown in Fig 4, the input end of the fiber bundle 116 is secured within a metal ferrule 138, which in turn is soldered or epoxied withm the axial bore of the body 136 Between the window 134 and the ferrule 138 is disposed a layer of adhesive 140, which adheres firmly to both the window and the ferrule, and which is chosen to have as high a thermal conductivity as possible, and to be essentially non- absorptive of the radiation passing through the window 134

The cell 118 is designed to allow efficient absorption by the input end of the fiber bundle 116 of the radiation from the lamp 110 without permitting the temperature of this input end to become so high that there is πsk of damage to the acrylic plastic fibers forming the bundle As already mentioned, the window 134 is designed to reject a large proportion of the non-visible radiation which would otherwise be absorbed within the input end of the bundle 116 and generate heat therein Thus, the window 134 reduces the amount of heat generated withm the input end of the bundle 116 Furthermore, the ferrule 138, the adhesive layer 140 and the window 134 all serve the remove heat rapidly from the input end of the bundle 116, thereby limiting the temperature πse thereof Finally, the cooling fins 120 (which, as shown in Fig 4, have the form of a senes of parallel radial flanges extending outwardly from the cyhndncal body 136), together with the air flow provided by the fan 20 (Fig 1) effect rapid removal of heat from the cell 118 Thus, the cell 118 enables the high intensity radiation from the lamp 110 to be efficiently channeled into the bundle 116 without damage to the plastic fibers forming this bundle Again, it may be preferable to randomize fibers withm bundles wherever sensible throughout the fiber delivery system so that a lamp failure has minimal impact on output uniformity Fig 5 shows a view, similar to that of Fig 4, of an alternate coupling cell 118' which can be used in place of the cell 118 shown in Fig 4 The cell 118' is used in conjunction with a lamp 110, side plates 124 and 126 and a vaπable aperture 132, all of which can be identical to the conesponding components shown in Fig 4 However, the coupling cell 118' comprises a hollow cylindrical body 136' which is of greater axial length than the body 136 shown in Fig 4, the body 136' also lacking cooling fins, though such fins could be added if desired Like the body 136 shown m Fig 4, the body 136' shown in Fig 5 has an axial bore The end of this bore, facing the lamp 110, is closed by a window 134', which need not be formed of sapphire, but which is provided on its outer surface with a heat reflecting dichroic coating to reduce the amount of ultraviolet and infrared radiation entenng the cell 118' The opposed end of the axial bore is closed by a metal plate 138', into which is secured a fiber bundle 116' However, as shown in Fig 5, the metal plate 138' has a much shorter axial length than the metal ferrule 138 (Fig 4), and the bundle 116' extends through the plate 118' for a substantial distance into the central portion of the cell 118'

The cell 118' lacks the adhesive layer 140 (Fig 4) of the cell 118 Instead, the intenor of the housing 136' is filled with a heat transfer and absorbing liquid 150, which is typically aqueous The liquid 150 may incorporate color absorbing or fluorescent substances to aid in color conection of the output from the lamp 110, the liquid 150 could also include, for example, infrared dyes to further reduce the amount of infrared radiation reaching the bundle 116' Some non-visible radiation still reaches the input end of the bundle 116', however, and is absorbed there, thus generating heat withm the input end of the bundle The fluid 150, which completely sunounds the input end of the bundle 116', serves to conduct heat away from the input end, thus preventing the temperature of this input end from reaching a level which adversely affects the plastic fibers forming the bundle 116' Although not shown in Fig 5, desirably the housing 136' is provided with ports through which the liquid 150 can be circulated out of the housing 136' and passed through a heat exchanger to cool the liquid If no precautions are taken, the liquid 150 tends to wick between the fibers of the bundle 116', thus adversely affecting the optical properties of the bundle.

To prevent such wicking, it is desirable that the gaps between the individual fibers of the bundle 116' be filled with a material (not shown in Fig. 5), such as a silicone, which is not wetted by the liquid 150.

The construction of the high optical LED assembly 36 of the invention shown in Fig. 1 will now be explained in detail with reference to Figs. 6-11. As already mentioned, Fig. 6 is an exploded perspective view of the light emitting diode assembly shown in Fig. 1, and should be viewed in conjunction with Fig. 8, which shows the actual assembled form of some of the components shown in Fig. 6. The LED assembly 36 comprises an LED 152 preferably formed as a single, continuous device approximately 2.5 mm square in a manner described below with reference to Fig. 9. The LED assembly 36 further comprises a transparent window 154 which is essentially the same size as, and is bonded directly to the front surface (as seen in Fig. 8) of the LED 152, so that the light leaving the LED 152 passes through the window 154. The window 154 may have a thickness in the range of about 0.1 to 1.0 mm, preferably 0.25 to 0.5 mm, and is desirably formed of a material having a refractive index closely matched (to within about ± 0.2) to that of the wafer of the LED 152 to which it is bonded, so that light from the anay 152 undergoes minimal deviation on passing through the window thereby operating to couple more light out of the wafer in a direction in which it is subsequently more easily managed for downstream use and experiences less total internal reflection (TIR). In addition, a close index match is desired to minimize unwanted Fresnel reflections. Arsenic trisulfϊde is the prefened material for forming the window 154. An insulator member 156 formed of a ceramic material has a central square aperture 158 passing therethrough, and (as best seen in Fig. 8) both the anay 152 and the window 154 are accommodated within this aperture 158. Although not shown in the accompanying drawings, the insulator member 156 is metallized, preferably with gold, to provide conductors which electrically contact conductors on the LED anay 152. The assembly 36 further compnses a hemispherical lens 160, the flat surface of which is mounted on the insulator member 156 and centered over the aperture 158 (see Fig 8) so that the center of curvature of the hemisphencal lens substantially coincides with the center of the LED 152 The combination of the window 154 and the hemisphencal lens 160 is designed to capture the largest possible fraction of the light leaving the LED 152 Such an anay emits light over one entire hemisphere, and the index-matched window 154 allows substantially all this light to pass through it undeviated, so that this light enters the flat base of the lens 160 and emerges substantially perpendicular to the part-sphencal surface of this lens Obviously, the fraction of the light emitted by the LED 152 which can emerge perpendicular to the part-sphencal surface of the lens 160 in this manner increases with the radius of the lens, and desirably this radius should be from about 2 to about 6 times the maximum width of the LED 152, further increases in lens diameter beyond this range increase the size and cost of the lens without any significant increase in efficiency in captunng light from the LED 152 With the prefened 2 5 mm square anay, a lens 160 having a radius of 7 mm has been found to give very satisfactory results The index of refraction of lens 160 preferably closely matched that of the window 154

Light emerging from the hemisphencal lens 160 is converged by means of an imaging lens assembly (generally designated 162) on to the input surface of a fiber optic bundle 164 which is preferably geometrically similar to the geometry of LED 152 The imaging assembly compnses four separate lens 166, 168, 170 and 172 The lens 166, closest to the hemisphencal lens 160, is a concave-convex lens having a concave surface facing the hemispheπcal lens 160 This concave surface is part- spherical and is substantially concentnc with the hemispheπcal surface of the lens 160 so that light emerging perpendicular to the part-sphencal surface of the lens 160 will also enter the lens 166 substantially perpendicular to its concave surface

Full details of the optical features and prescπption of the imaging lens assembly 162 are as follows GENERAL LENS DATA System Aperture: Object Space N.A. = 2 Glass Catalogs: Schott MISC INFRARED O'Hara Ray aiming: Off Apodization: Uniform, factor = 0.00000E+000 Eff Focal Len.: -45.85728 (in air) Eff. Focal Len.: -45.85728 (in image space) Back Focal Len.: 236.691 Total Track: 129.203 Image Space F/#: 1.370045 Para. Wrkng F/#: 0.7040986 Working F/#: 1.017714 Image Space N.A. 0.5789912 Obj. Space N.A.: 2 Stop Radius: 38.78824 Parax. Ima. Hgt.: 5.685729 Parax. Mag.: -4.373638 Entr. Pup. Dia.: -33.47136 Entr. Pup. Pos.: -14.33618 Exit Pupil Dia. : 301.17 Exit Pupil Pos.: -208.6992 Field Type: Object height in Millimeters Maximum Field: 1.3 Primary Wave: 0.623 Lens Units: Millimeters Angular Mag.: -0.2905299 SURFACE DATA SUMMARY:

Lens # Surf. Type Radius Thickness Glass

Diameter

OBJ STANDARD 8 0.25 As₂S₃-EXT

2.6

160 1 STANDARD 8 8 < LEARTRAN

3.240191

160 2 STANDARD -7 9.853397 Air 13.6

166 3 STANDARD -21.2 14.98527 SFL57 31

166 4 STANDARD -22.92 0.2490852 Air 44

168 5 STANDARD -101.07 10.72039 SF1 1 58

168 6 STANDARD -46.35 -15.93114 Air 62

STO STANDARD 8 16.93091 Air

57.53414

170 8 STANDARD 161.12 10.27719 SF11 68

170 9 STANDARD -161.12 30.53356 Air 68

172 10 STANDARD 33.791 10.81073 SF1 1 51

172 1 1 STANDARD 66.515 32.77365 Air 47 The overall lens systems comprising the lens 160 and the lens assembly

162 is designed so that the LED 152 which as already mentioned is 2.5 mm square, and has a numerical aperture of 2, is coupled into the fiber optic bundle 164, which is 11.8 mm square and has a numerical aperture of 0.5. The calculated coupling efficiency for coupling between the anay 152 and the bundle 164 is approximately 96 per cent. Fig. 6 also illustrates the components provided for removing heat generated within the LED 152. The components comprise a heat spreading member in the form of a 10 mm square substrate 174 formed of polycrystalline diamond which has a very high thermal conductivity as, for example, that marketed under the trade name of Diamonex by Diamonex, Inc., Allentown, PA. The side of the LED 152, remote from the window 154, is secured directly to the substrate 174, and the opposed side of the substrate 174 is mounted directly upon a heat removal device 176, which is a Therma-Cube™ heat exchanger as, for example, those marketed by Thermocore, Lancaster, PA. Heat removal device 176 is essentially a metal cuboid with internal microchannels through which cooling fluid is circulated by the two pipes shown in Fig. 6 and elsewhere at 173 and 175. Heat removal device 176 may also be in the form of an appropriately configured thermoelectric cooler. Fig. 9 shows the detailed construction of the LED 152. Unlike prior art anays such as that illustrated in the aforementioned '689 application, the LED 152 is not formed by assembling a number of discrete LEDs, but rather is formed by creating at least one pair of electrodes on opposed surfaces of a single, continuous semiconductor substrate 178, which is formed in known manner so that it will emit light when cunent flows from one of its major surfaces to the other. More specifically, the upper surface (in Fig. 9 - this being the surface facing the hemispherical lens 160 shown in Fig. 6) of the substrate 178 is metallized (by any of the conventional metallization techniques well-known to those skilled in the semiconductor art) to form thereon a pair of rails 180 extending along one opposed pair of edges of the upper surface, and five elongate conductors 182 extending between these rails 180. From each lateral edge of each of the conductors 182, there extend normally to the conductor, at regularly spaced intervals, ten small projections 184 making for a device with a 10 X 10 anay of emitting areas. It is these projections 184 which serve as the actual electrodes of the LED 152. The undersurface of the wafer 178 is metallized in a similar manner, but without any masking so that it is formed as a continuous electrode. The rails on the two major surfaces of the wafer 178 are connected to an external voltage source, thus establishing a potential difference between the metallized areas on these two surfaces which causes cunent to flow ("injection cunent") between each of the projections 184 and the conesponding electrode on the undersurface of the substrate 178. As will be apparent to those skilled in electrodynamics, the resultant cunent will not only flow through those parts of the substrate lying directly between the projections but rather, because of the repulsion between like charges, will extend a significant distance beyond the periphery of each projection, the overall shape of the cunent flow resembling a distorted ellipsoid. This "extension" of current flow beyond the periphery of the projections 184 will cause light to be emitted from the same area so that, while the potential difference is applied, each of the projections will be sunounded by a substantially circular area (in effect, a single LED emitting area) from which light escapes via the upper surface of the wafer 178. Thus, since the emitting surface of the substrate 178 is provided with one hundred projections 184, the substrate functions as a more or less continuous emitting area. It has been found that a single 2.5 mm continuous device square wafer formed as such has a light output sufficient to provide 5 Watts optical into the fiber bundle 164 (Fig. 6). The electrical power required to provide such a 5 W output does not exceed about 30 W, in contrast to the 150 W needed to provide the same output using a conventional array of discrete LEDs. It will readily be apparent to those skilled in the art of semiconductor fabrication that the number and arrangement of the LED provided on a substrate similar to substrate 178 shown in Fig. 9 can be varied. The total number of emitting areas can vary from a (practical) minimum of 9 or 16 up to several hundred, since appropriate light-emitting semiconductor wafers are commercially available in sizes much larger than the 2.5 mm square size described above. Care must be taken in the design of the metallizations so that each emitting area experiences approximately the same injection cunent within acceptable limits, say within 5% of one another.

Figs. 10 and 11 illustrate alternative patterns of metallization which may be substituted for that shown in Fig. 9. The so-called "hour-glass" pattern shown in Fig. 10 closely resembles that shown in Fig. 9, but instead of the conductors 182 being rectangular as in Fig. 9, the conesponding conductors 182' shown in Fig. 10 vary in width, being "necked" to form narcow sections at their intersections with the projections 184'. Depending upon the exact dimensions of the various components of the LED anay 152 shown in Fig. 9 and the operating conditions employed, the circular light-emitting areas may tend to extend beneath the lateral edges of the conductors 182 where these conductors join the projections 184, with the result that the lateral edges of the conductors 182 obscure parts of the light-emitting areas, thus reducing the total light output from the device. The pattern shown in Fig. 10 seeks to avoid this problem by, in effect, removing those portions of the lateral edges of the conductors 182' likely to obscure the light-emitting areas.

The pattern shown in Fig. 11 is designed to produce a more uniform areawise output from the LED. In this pattern, the rails elongate conductors 182 shown in Fig. 9 are replaced by a rectangular grid of conductors 186, which leave square apertures therebetween. Cruciform projections 188 extend into these apertures and serve as the electrodes of the LED. These cruciform electrodes 188 produce emission patterns centered on the centers of the square apertures at the centers of the cruciform electrodes, so that the amount of light-emitting area obscured by the electrodes and the conductors 186 is kept to a minimum. Regardless of the pattern used, the high optical power LED of the present invention may be constructed of various semiconductor material systems comprising well-known layers of doped p and n type materials depending on the desired operating wavelength. For the surgical illumination system illustrated, the prefened material is GaAlAs and the operating wavelength is 625 nm. In addition to the various metallization patterns illustrated, it will be appreciated that the far field illumination pattern being emitted collectively by all of the emitting areas of the LED may be influenced by the spacing between individual emitting areas, their size, and overlapping radiation patterns. Thus, one may achieve a relatively flat far field pattern where Gaussian patterns being emitted by individual emitting areas are ananged to overlap one another.

The function of the window 154 can be provided by depositing a layer of material of suitable index of refraction directly on the emitting surface of the LED and then optically polishing that surface. Such a layer may be formed by vapor deposition or the like. In place of the prefened single continuous device, it will evident that an anay of discrete LED's of lower power that have been closely packed and electrically stitched together may be used and then combined with the other elements of the invention in the manner previously described.

Fig. 12 shows schematically the components of the light mixer/feedback module and variable aperture/shutter module shown in Fig. 1. As shown in Fig. 8, the fiber optic bundle 32 (see Figs. 1 and 3) carrying light from the lamp assembly 18 and the fiber optic bundle 38 (see Figs. 1 and 6) carrying light from the LED assembly 36 are combined to form a single bundle 190, in which the individual fibers from the bundles 32 and 164, if required, may be randomly distributed. The combined bundle 190 is joined by means of a butt joint to an optical homogenizer in the form of a multimode light pipe 192 formed from a single rod of transparent plastic material, the length of the light pipe 192 is reduced in Fig 12 for ease of illustration (Those skilled m the art of optical fibers will be aware of various conventional techniques for reducing light losses from butt joints such as that between the bundle 190 and the light pipe 192, for example the provision of a reflective collar sunoundmg the butt joint, accordingly such conventional techniques for reducing light loss from joints will not be further discussed herein ) The light pipe 192 intermingles the outputs from the individual fibers in the combined bundle 190 so that the output from the homogenizer is (except for losses withm the fiber optic bundles and at the vaπous interfaces, the sum of the inputs to the bundles 32 and 164 from the lamp assembly 18 and the LED assembly 36, respectively As previously mentioned, the appropπate mixing of the blue-biased light from the lamp assembly 18 with the red-biased light from the LED assembly 36 produces light having a proper CCT and CRI for surgical lighting

Also as already mentioned, in some cases the outputs from metal halide lamps and LED's is sufficiently stable so that once the proper balance between the metal halide lamps and the LED's has been set by adjusting the vanable apertures 132 (Fig 4) or cunent to LEDs, the lighting from the illumination system 10 will maintain a proper CCT and CRI for an extended penod If, however, it is desired to provide a feedback loop to enable real-time adjustment of the balance from the two light sources 18 and 36, this can be achieved using the apparatus shown in Fig 12 As shown in that Figure, the light pipe 192 is provided, near its outlet end, with a pick-off member 194, which is inserted into a small radial bore formed in the light pipe, such that the pick-off member 194 directs a sample of light from the axis of the light pipe 192 into a spectral analyzer 196 The output from this spectral analyzer 196 is fed to a computing unit 198, which calculates the CRI of the light from the spectral data supplied by the analyzer 196, although the CRI should in theory be calculated in terms of an average color shift of eight standard colors, as discussed above, in practice a simpler calculation, involving measurement of spectral intensity at a smaller number of wavelengths, for example five or six, may often prove sufficiently accurate, and thus the present invention is not limited to using the stπct CRI calculation withm the computing unit 198. The output from the computing unit 198 is fed to a color mixing module 200, which may control (via the control module 42 shown in Fig. 1) the settings of the variable apertures 132 (Fig. 4) of the lamp assembly 18; as previously noted. Control of lamp output by variable apertures in this manner, rather than by controlling the power input to the lamps, ensures that the adjustment of lamp output is not accompanied by the spectral changes normally experienced when lamp output is controlled by varying power input. However, cunent to the LEDs may also be varied for this purpose.

The output end of the light pipe 192 is disposed adjacent the input end of the fiber optic bundle 46 (cf. Fig. 1) which canies the light from the variable aperture/shutter module 44 to the light splitter 48 disposed within the operating room section of the illumination system 10. A variable aperture 202 is disposed between the light pipe 18 and the bundle 46, this variable aperture 202 being used to control the overall light intensity provided by the illumination system. Typically, the variable aperture 202 is power operated and under the control of the control module 22 (Fig. 1).

In an alternative apparatus shown in Fig. 13, the bundles 32 and 164 are combined to form a bundle 190'. However, the fibers from the bundles 32 and 164 are not randomized within the combined bundle 190', and all the necessary homogenization of the light occurs within the light pipe 192; this approach is generally prefened because is greatly simplifies assembly of the bundles 32, 164 and 190'. As in the apparatus shown in Fig. 12, the combined bundle 190' is joined by means of a butt joint to an optical homogenizer in the form of a multimode light pipe 192'. Whereas the light pipe 192 shown in Fig. 12 is normally a simple cylindrical rod, the light pipe 192' shown in Fig. 13 has the form of a regular polygonal prism. Good results have been obtained from an undecagonal prism having eleven lengthwise facets on its circumferential surface as shown in Fig. 13; the number of facets is not critical, but is chosen on the basis of the diameter needed to couple to all of the fibers in the upstream bundle 180', the length of the light pipe 192' and so that the area of mismatch with the nominally circular downstream bundle 46 is minimal. Those skilled in the art of designing optical systems will be aware that in such a polygonal prismatic light pipe of given length and maximum cross-section, there is an optimum number of facets which will produce the most effective mode mixing withm the light pipe, and obviously the light pipe 192' should be designed with the optimum number of facets

The use of a polygonal prismatic rather than cylindrical light pipe 192' is also advantageous in secuπng uniform distπbution of light among the fibers of the bundle 46 which receives the output from light pipe 192' Those skilled in optics are aware that when light passes along a lengthy cyhndncal light pipe, adjacent the output end of the pipe the intensity of the light vanes radially of the pipe The resultant radial variation of light intensity withm the light pipe is undesirable, since it produces a conesponding radial variation m light intensity withm the fibers of the bundle 46, and may produce undesired vaπations in the light intensity within the area to be illuminated In effect, the radial vanation in intensity withm a cyhndncal light pipe 192 may create zones withm bundle 46 receiving less light than others Use of a polygonal pnsmatic light pipe 192' reduces or essentially eliminates any radial vaπation of light intensity at the output end of the light pipe, thus rendeπng more uniform the intensity of light fed to the various fibers withm bundle 46

The two approaches to homogenization of light withm the bundles 32, 164 and 190 and the light pipes 192 and 192' descπbed above with reference to Figs 12 and 13 respectively are not, of course, mutually exclusive Depending upon the specific apparatus and degree of uniformity of light output desired, one could effect partial or complete randomization of the fibers with the combined bundle 190 and still use a polygonal pπsmatic or similar light pipe 192' to effect further homogenization of the light and avoid the problems associated with a cyhndncal light pipe, as discussed above The apparatus shown in Fig 13 also differs from that shown in Fig 12 in the construction of its feedback anangement The light pipe 192' is provided, near its outlet end, with two pick-off members 194' and 195' Each of these pick-off members 194' and 195' has the form of a cyhndncal rod approximately 1 mm in diameter and terminated at its lower end by a slanting facet cut at 45° to the axis of the cylindrical rod, these slanting facets are alummized so that each pick-off member diverts a sample of the light passing along the light pipe 192' along the axis of its pick- off member 194' or 195' The pick-off members 194' and 195' are placed withm the light pipe 192' using known techniques, preferably two radial bores are formed m the light pipe, and the pick-off members, with the slanting faces already alummized are secured withm these radial bores using index matching cement The numerical apertures of pick-off members 194' and 195' are preferably made greater than 0 48

The output from pick-off member 194' falls directly on a detector 199 A, but the output from pick-off member 195' first passes through a filter 197 and then falls on a detector 199B The detector 199A thus receives a sample of all the light passing along the light pipe 192' However, the filter 197 is ananged to pass only the red portion of the visible spectrum (numerous appropnate filter mateπals are known to those skilled in the art, the presently prefened mateπal for the filter 197 being Schott RG610 glass, so that the detector 199B receives only red light passing along light pipe 192', this light oπginatmg pπmanly from the LED assembly 36 (Fig 1) The detectors 199A and 199B are photovoltaic detectors, preferably with an active area approximately 5 mm in diameter when using 1 mm diameter pick- off members 194' and 195 The output from detector 199A is fed to an amplifier 201 A, with vaπable gam, while the output from detector 199B is fed to a second amplifier 20 IB, with fixed gam The outputs from the amplifiers 201 A and 20 IB are fed to the two inputs of a differential amplifier 203, the output from which is proportional to the difference between its two inputs, I e , to the difference between the outputs from the amplifiers 201 A and 20 IB The output from the differential amplifier 203 is fed to a color mixing module 205, which may control (via the control module 42 shown in Fig 1) the settings of the variable apertures 132 (Fig 4) of the lamp assembly 18, as previously noted The color mixing module 205 controls the relative outputs from the lamp assembly 18 and the LED assembly 36 until the difference between the outputs of the two detectors 199A and 199B is dπven to zero, thus, the ratio of the light incident on the two detectors 199A and 199B is controlled so that signals from the detectors are inversely proportional to the ratio of their amplifier gains To show the manner m which the equipment illustrated in Fig 12 controls the output from the lamp assembly 18 or the LED assembly 36, the following simplified analysis is presented It will be apparent to those skilled in the art that a similar analysis could be used if the amplifiers 201 A and 201B were interchanged, so that it would be the output from the detector 199B which was subject to the vaπable gam The following analysis assumes that both detectors 199A and 199B have identical and uniform spectral power distributions (SPD's)

Let

P_L be the lamp power incident on the first detector 199A, P_D be the LED power incident on each detector (this power is the same for both detectors, k be the lamp power incident on the second detector 199B,

Si and S₂ be the signals from the first and second detectors respectively,

R be defined as SJS₂, and r be defined as P_L/P_D

Then

S , = P_L + PD (1)

S₂ = kP_{L +} P_D (2) Substituting for Si and S in Equations (1) and (2) R = (P_L + P_D)/(kP_{L +} P_D) (3)

R = ([PL/PD] + l)/(k[P_L/P_D] +l) (4)

R = (r + l)/(kr + l) (5) r = (R-l)/(l - k + R) (6)

Thus, if the signal ratio R is kept constant, then r remains constant (Note that, from Equation (6), if k = 1 no useful information is obtainable')

To see the effect of k on system performance, define a new vanable R' as the ratio of amplifier gams as discussed above Assume upon an initial calibration R = R', and r = 3 Next assume that R' increases by 1 percent. The following Table shows how the value of k affects r for this 1 percent increase in R':

For the present prefened apparatus Welsh Allen lamps and a 10 meter SPD, and the prefened Schott RG610 filter material, k is approximately 0.16, and at this k value, a 1 percent change in R' conesponds to a change in r of less than 2.6 percent. Since experimentally it has been determined that with the Welsh Allen lamp and LED's operating at 632 nm, the system gives satisfactory CCT and CRI if r is held constant to ±15 percent, the design allows for considerable variation in R while still maintaining satisfactory output. If the SPD's of the two detectors 199A and 199B are not uniform and different from one another, Equation (3) becomes:

R = (aP_L + bP_D)/(dkP_{L +} cP_D) (7) where a, b, c and d are constants, while Equation (6) becomes: r = (b - Rc)/(Rkd - a) (8) Again, if R is held constant, r will remain constant. Furthermore, enor analysis indicates that for: k = 0.2 r = 3 a = l b = 1.5 c = 1.2 and

(1 = 1.8, a 1 percent change in R produces a 5 percent change in r, again well within tolerable limits.

The apparatus shown in Fig. 13 is not intended for initial calibration of the apparatus, but only for "running adjustment" of the light output as the lamps and LEDs ago, or other factors cause minor changes in light output, For initial calibration, it is generally desirable to use a spectral analyzer adjacent the output end of light pipe 192' and carry out a detailed spectral analysis in order to ensure optimum adjustment of the CCT and CRI of the output light. In carrying out such a spectral analysis, it should be noted that, although the CRI should in theory be calculated in terms of an average color shift of eight standard colors, as discussed above, in practice a simpler calculation, involving measurement of spectral intensity at a smaller number of wavelengths, for example five or six, may often prove sufficiently accurate, and thus the present invention is not limited to using the strict CRI calculation to effect calibration of light output. It will be appreciated that the sampling bandwidth should be sufficiently small to capture any source lines that are prominent enough to contribute significantly to color content.

The output end of the light pipe 192' is disposed adjacent the input end of the fiber optic bundle 46, associated with a variable aperture 202; these components operate in exactly the same manner as described above with reference to Fig. 12. Alternative terminations to the surgical lighting systems described are shown in Figs. 15 and 16. In Fig. 15, a fiber based surgical lighting system 500 has light heads 502 and 504 that operate in the manner previously described having light delivered to them via the fiber distribution architecture detailed above. System 500 differs from those previously described in that one branch of the fiber distribution system that would usually feed a light head instead terminates in a connector hub 506 that is provided with an articulated arm 508 that has an interface for connecting a fiber bundle 510 that provides light to a surgical head lamp 512. One or more universal mounting adapters can be provided at the distal end of an articulated arm to feed one or more surgical head lamps. Such universal fiber connectors are readily commercially available to interface with commercially available fiber bundles from, for example, Storz, Wolf, ACMI, and Olympus Relative to existing art, this system has the advantage of including improved color rendering and color temperature performance which is consistent with the spectral character of surgical lamps, reduced clutter on the floor relative to rack mounted light sources and reduced fatigue for the surgeon due to the lower weight of the light guide There are cunently no guidelines, such as that for over-the-table surgical lights (IEC-601-2-41), for color temperature and color rendering of surgical head lamps and endoscopes This could result m enors in identification of anatomical features with grave consequences This system would be the first step toward assuring consistent and accurate color identification for illuminated surgical procedures

Fig 16 shows a system 600, similar in concept to system 500, except for dehvenng light to one or more endoscopes As before, system 600 has light heads 602 and 604 and a connecting hub 606 carrying standard connectors for receiving fiber bundles 608 and 610 that feed endoscopes 612 and 614, respectively It should be appreciated that systems 500 and 600 can be readily adapted to interface with head lamps and/or endoscopes and that one or more connecting ports having articulated arms or not may be used

From the foregoing descπption, it will be seen that the present invention provides a light source, and an LED for use in such a light source, which greatly simply the assembly of the LED as compared with the assembly of conventional LED from numerous discrete LED's The light source of the present invention can generate a high light output using less power than pnor art LED anays, thus simplifying the problem of cooling the anay The LED of the present invention can readily be fabncated by conventional semiconductor fabπcation techniques in an economical manner

While the invention has been descnbed with reference to particular embodiments thereof, those skilled in the art will be able to make vaπous modifications to the descπbed embodiments of the invention without departing from its true spirit and scope For example, it will be apparent that the microchannel cooling module may be replaced with a thermo-electric type cooler of suitable capacity. Other changes will apparent and are intended to be within the scope of the following claims.

Claims

What we claim is: 1. A light source comprising: an LED ananged to emit light through an exit surface; a transparent window secured to said exit surface; and a lens having substantially the form of part of a sphere, said part- spherical lens being disposed on the opposed side of said window from said LED, and the center of curvature of said part-spherical lens being disposed on or adjacent said LED. 2. A light source according to claim 1 wherein said LED comprises a semi-conductor substrate having first and second surfaces on opposed sides thereof and also having light-emission characteristics such that flow of current from the first to the second surface of the substrate will cause light to be emitted from said substrate, said LED further comprising at least one pair of electrodes, one of each pair being disposed on said first and the other on said second surface of said substrate, whereby application of a potential difference between the electrodes of said at least one pair of electrodes causes flow of current through said substrate and emission of light from discrete areas of said substrate lying between said electrodes, thereby causing said substrate to act as said plurality of light-emitting diodes and emit light from said first surface of said wafer, which first surface forms said exit surface of said LED. 3. A light source according to claim 2 wherein said at least one pair of electrodes are formed by metallizing said first and second surfaces of said substrate. 4. A light source according to claim 2 wherein at least one of said first and second surfaces of said substrate is provided with an elongate conductor having a plurality of projections extending at spaced intervals laterally from said conductor, said projections forming said electrodes. 5. A light source according to claim 4 wherein said one of said first and second surfaces of said substrate is provided with a plurality of elongate conductors extending substantially parallel to each other and each provided with a plurality of projections extending at spaced intervals laterally from the conductor, said projections forming said electrodes.

6. A light source according to claim 5 wherein said projections extend substantially normal to said elongate conductors from both sides thereof. 7. A light source according to claim 5 wherein said projections are ananged to form a rectangular grid of light-emitting diodes. 8. A light source according to claim 2 wherein said substrate is formed of gallium nitride. 9. A light source according to claim 1 wherein said window has a refractive index which closely matches the refractive index of said LED whereby light emerging from said exit surface of said LED undergoes minimal deviation on passing through said window. 10. A light source according to claim 9 wherein said LED comprises a gallium nitride substrate and said window is formed from arsenic trisulfide. 11. A light source according to claim 1 wherein said window has a thickness in the range of from about 0.1 to about 1.0 mm. 12. A light source according to claim 1 wherein said lens has substantially the form of a hemisphere and an index of refraction that closely matches that of said window. 13. A light source according to claim 1 wherein the diameter of said lens is from about 2 to about 6 times the maximum width of the LED. 14. A light source according to claim 1 further comprising heat removal means for removing heat generated within said LED. 15. A light source according to claim 14 wherein said heat removal means comprises a heat spreading member having high thermal conductivity and secured to said LED assembly on the opposed side thereof from said exit surface, and a heat removal device in thermal contact with a surface of said heat spreading member remote from said LED assembly. 16. A light source according to claim 15 wherein said heat spreading member is formed from polycrystalline diamond. 17 A light source according to claim 15 wherein said heat removal device comprises a member provided with microchannel fluid flow means for passing a fluid therethrough 18 A light source according to claim 1 further compnsmg an insulator member formed from an electncally-insulatmg matenal and having walls defining an aperture with which said LED is accommodated, said insulator member being provided with electπcal conductors in electπcal contact with conductors of said LED 19 A light source according to claim 1 further compnsmg an imaging lens assembly ananged to receive light from said part-sphencal lens and to focus said light on to a restncted focal area 20 A light source according to claim 19 wherein said imaging lens assembly compnses a concave-convex lens element disposed adjacent said part- sphencal lens and having a concave surface facing said part-sphencal lens, said concave surface having the form of part of a sphere substantially concentnc with the sphere defined by the part-sphencal lens 21 A light source according to claim 20 further compnsmg at least one optic fiber having an input end disposed at or adjacent said focal area to receive light from said LED anay focused by said imaging lens assembly 22 A lighting device comprising a light source according to claim 21 having a fiber optic bundle disposed at or adjacent said focal area to receive light from said LED focused by said imaging lens assembly, a second light source having a spectral distnbution different from that of said LED, at least one light pipe or fiber optic bundle ananged to transmit light from said second light source, and mixing means for mixing the light from the LED with that from said second light source to produce a mixed light beam 23 A lighting device according to claim 22 wherein said second light source is an incandescent light source

24. A lighting device according to claim 22 further comprising at least one lighting head ananged to output light from said mixed light beam to an area to be illuminated. 25. An LED comprising at least one semi-conductor substrate having first and second surfaces on opposed sides thereof and also having light- emission characteristics such that flow of cunent from the first to the second surface of the substrate will cause light to be emitted from said substrate, said LED further comprising at least one pair of electrodes, one of each electrode being disposed on said first and the other on said second surface of said substrate, whereby application of a potential difference between the electrodes causes flow of cunent through said substrate and emission of light from discrete areas of said substrate lying between each of said at least one pair of electrodes, thereby causing said substrate to act as a plurality of light-emitting diodes and emit light from said first surface of said substrate. 26. An LED according to claim 25 wherein said at least one pair of electrodes is formed by metallizing said first and second surfaces of said substrate. 27. An LED according to claim 25 wherein at least one of said first and second surfaces of said substrate is provided with an elongate conductor having a plurality of projections extending at spaced intervals laterally from said conductor, said projections forming said electrodes. 28. An LED according to claim 27 wherein said one of said first and second surfaces of said substrate is provided with a plurality of elongate conductors extending substantially parallel to each other and each provided with a plurality of projections extending at spaced intervals laterally from the conductor, said projections forming said electrodes. 29. An LED according to claim 28 wherein said projections extend substantially normal to said elongate conductors from both sides thereof. 30. An LED according to claim 28 wherein said projections are ananged to form a rectangular grid of light- emitting diodes. 31. An LED according to claim 25 having at least sixteen pairs of said electrodes.

32. An LED according to claim 25 wherein said substrate is formed of gallium nitride. 33. An LED according to claim 25 having a transparent window secured to its first surface. 34. An LED according to claim 33 wherein said window has a refractive index which closely matches the refractive index of said substrate, whereby light emerging from said first surface of said substrate undergoes minimal deviation on passing through said window. 35. An LED according to claim 33 wherein said window has a thickness in the range of about 0.1 to about 1.0 mm. 36. An LED according to claim 33 wherein said window is formed from arsenic trisulfide. 37. An LED according to claim 25 further comprising an insulator member formed from an electrically-insulating material and having walls defining an aperture with which said wafer is accommodated, said insulator member being provided with electrical conductors in electrical contact with conductors of said LED. 38. An LED according to claim 25 further comprising heat removal means for removing heat generated within said LED. 39. An LED according to claim 38 wherein said heat removal means comprises a heat spreading member having high thermal conductivity and secured to said LED assembly at a point spaced from said first surface, and a heat removal device in thermal contact with a surface of said heat spreading member remote from said LED assembly. 40. An LED according to claim 39 wherein said heat spreading member is formed from polycrystalline diamond. 41. An LED according to claim 39 wherein said heat removal device comprises a member provided with microchannel fluid flow means for passing a fluid therethrough.