WO2006122714A1

WO2006122714A1 - Multispectral lighting unit

Info

Publication number: WO2006122714A1
Application number: PCT/EP2006/004474
Authority: WO
Inventors: Lutz HÖRING; Andreas Nolte
Original assignee: Carl Zeiss Jena Gmbh
Priority date: 2005-05-13
Filing date: 2006-05-12
Publication date: 2006-11-23
Also published as: DE102005022175A1

Abstract

The invention relates to a lighting unit which allows to light objects with white light or light of a different defined wavelength in a very homogeneous manner. The inventive multispectral lighting unit is based on a spectrometer assembly wherein the photodetector is replaced by a linear arrangement of LEDs (4) emitting light of different wavelengths and being controlled individually via current regulators. The light emitted by the LEDs (4) that are spectrally arranged according to their peak wavelengths is coupled into an optical fiber (1) and/or illumination optics by a spectrally selective component and mixed therein, thereby producing spectrally and laterally homogeneous light that emerges at the output thereof. The inventive lighting unit can be generally used in all applications that require spectrally controllable, homogeneous light sources the lighting conditions of which can be varied extremely quickly and precisely. Possible fields of application are for example microscopy and endoscopy. The invention provides a very compact, almost freely switchable multispectral lighting unit that can be spectrally controlled by means of electronics.

Description

Multispectral lighting unit

The present invention relates to a lighting unit with which objects can be illuminated as homogeneously as possible with white light or light of another defined wavelength. The change of lighting conditions can be extremely fast and precise, without any, mechanically moving parts.

The conventional light sources known in the prior art emit characteristic spectra corresponding to the mode of light generation. For example, halogen lamps that are Planckian emitters emit spectrum that varies with the applied electrical current, and the spectrum shifts to lower wavelengths for larger currents. While high pressure steam lamps emit an emission spectrum from discrete lines, the substantially continuous spectra of xenon-mercury lamps have pronounced local peaks. Laser sources produce high coherence monochromatic light.

In order to produce any spectral distribution with the known illumination systems, either filter systems or spectrometers for the selection of individual wavelengths are required.

The combination of multiple sources usually leads to an inhomogeneous illumination of the examination subject, which must be compensated by usually complex and difficult to adjust optical systems.

The disadvantages of conventional illumination sources are, for example, limited spectral diversity, inertia when changing the illumination states and the rather considerable thermal load. In the case of the white light source with light-emitting diodes for endoscopes described in EP 120 01 179 B1, the light source consists of at least two light-emitting diodes which emit light in different, preferably mutually complementary, spectral ranges, so that spectrally additive mixed light emerges from the illumination system. In an advantageous embodiment, three light emitting diodes are used as the white light source, which emit light of high light intensity preferably in the blue, green and red spectral range. Light emitting diodes (LED's) offer the advantage due to their small size that they are usually integrated into the device and can be dispensed with an external lighting unit. LEDs are now available with high brightness, so they are sufficiently bright for many applications. The LEDs can be pulsed as well as continuously, individually or jointly controlled. LEDs also have the advantage that in the case of the application of colored light, the color quality of light of a light emitting diode is better than when a white light source is used with a color filter.

US Pat. No. 5,489,771 A describes a standard LED light source as a calibration system for photographic and video microscopy. The standard LED light source can be used to determine the performance of the microscope optics or to calibrate the microscope system. Selectable light intensities are generated by controlling the energy supplied to the LEDs. In order to homogenize the preferably green, yellow and red light emitted by the LEDs, the LEDs are encapsulated in a diffuser. A portion of the light from the LEDs is scattered to the side and strikes a photodiode arranged there, the signal of which is provided to a control circuit to control the light intensity of the LEDs. This method of regulation automatically takes into account changes in the performance of the LEDs. The targeted activation of a defined light spectrum, such as monochromatic light can be generated that can be both continuous and pulse-modulated. A variable, multicolor LED lighting system for ophthalmic applications is described in US 6,183,086 B1, whose color of the emitted light can be varied. Compared to conventional ophthalmic lighting systems, less heat is emitted from the LEDs and a much longer life is achieved. The system consists of three LEDs of different colors, whose radiated light is mixed by a device and passed through an optical fiber to the ophthalmic device. Preferably, the color combinations are used: red-blue-green or red-blue-yellow. In addition to the white light produced by mixing the light components, the system can also be used to generate specific colored light for lighting through targeted control.

An LED based lighting unit for a surveillance system is described in US 6,624,597 B2. For the lighting system, the use of different colored LED's is provided, which are driven by a processor accordingly to produce white or colored light. Since previous, monochrome monitoring systems were essentially only suitable for determining size and shape, color systems can be used to control significantly more properties of the object to be monitored. The monitoring system described is based on a camera, a lighting unit and a processor that controls the illumination of the object to be analyzed accordingly. The control can be done for example by modulation of pulse width, intensity or other parameters. By creating a variety of colors, the lighting can be adapted to the particular object, the environment and the camera to provide optimal results. In addition to continuous illumination, strobe effects can also be realized with the system, which are used in particular on conveyor belts to make changes visible immediately. The LED-based lighting unit even allows monitoring in the ultraviolet or infrared spectral range. While many items can fluoresce under UV light and thus be easily labeled, they are monitored under IR light invisible spectral range. Lighting conditions can be changed almost instantaneously to provide a fast system response.

The present invention has for its object to develop a simple and compact illumination system with a spectrally adjustable light source, with which an object field can be illuminated as homogeneously as possible. The lighting system should be characterized by a high spectral diversity, a low inertia and low thermal problems.

According to the invention the object is solved by the features of the independent claims. Preferred developments and refinements are the subject of the dependent claims.

The lighting unit according to the invention can in principle be used everywhere where spectrally controllable, homogeneous light sources are required whose lighting conditions can be changed very quickly and precisely. Possible applications include microscopy and endoscopy.

The invention will be described below with reference to an embodiment. Show this

1 shows the basic structure of an MMS spectrometer,

FIG. 2: a selection of LED spectra (between 370 nm and 960 nm),

FIG. 3 shows a multispectral illumination unit based on a spectrometer arrangement according to the invention,

Figure 4: a programmable circuit arrangement for LED control and FIG. 5 shows an inventive multispectral illumination unit based on a monochromator arrangement.

In the case of the multispectral illumination unit based on a spectrometer arrangement, instead of the photodetector, a linear array of LEDs emitting light of different wavelengths and driven individually by current regulators is present, the LEDs being spectrally ordered according to their emitted peak wavelength. Their emitted light is coupled by a spectrally selective component in an optical fiber and / or illumination optics and mixed in this, so that emerges at the output spectrally and laterally homogeneous light.

To illustrate the inventive solution, Figure 1 shows the basic structure and beam path of an MMS spectrometer.

The measuring light reflected by the object is coupled in via an optical fiber 1 and split into its spectral components by the spectrometer-selective crystal 2 serving as a spectrally selective component and imaged on the photodetector 3. The simultaneously registered spectral components of the measuring light are evaluated accordingly.

Replacing the photodiode array with a linear arrangement of several LED's, one can use this arrangement as a source of illumination. The LEDs emit a narrowband light spectrum with a clear peak wavelength. FIG. 2 shows a selection of LED spectra (between 370 nm and 960 nm). It can be seen that LED's can produce light of a variety of wavelengths.

By, according to their peak wavelength spectrally ordered LED's it is achieved that the light emitted by the LEDs emitted light is coupled to a large extent in the optical fiber and / or illumination optics. In this, the light is mixed, so that emerges at its output spectrally and laterally homogeneous light.

Due to the small size of the individual LEDs of about 300 .mu.m, it is possible to provide a plurality of LEDs spectrally sorted according to their peak wavelength, so that a large part of the emitted light is coupled into the optical fiber and / or illumination optics. The larger this proportion, the lower the energy losses occurring. Likewise, it is also possible to use LEDs with a size of z. B. 1mm to increase the intensity of the source accordingly.

A multi-spectral illumination unit based on a spectrometer arrangement is shown in FIG. In this case, instead of the photodetector 3 (in FIG. 1), there is a linear arrangement of LEDs 4, which emit light of different wavelengths and are individually controlled via current regulators. The spectrally arranged LEDs 4 corresponding to their peak wavelength ensure that the emitted light from the spectrometer crystal 2 serving as a spectrally selective component is to a large extent coupled into the optical fiber 1 or illumination optics. Since the real, acting as a spectrally selective device spectrometer crystal 2 has a flat contact surface for the photodetector 3, it is also no problem to adapt there applied to a carrier board LED's 4.

To increase the efficiency of the illumination, one will increase the diameter of the optical fiber 1 or illumination optics over the spectrometer array. The light emitted by the applied LEDs 4 light is coupled from the spectrometer crystal 2 in the optical fiber 1 and mixed in this, so that emerges at the output spectrally and laterally homogeneous light. The LEDs are individually controlled by current regulators, which makes it possible to set a desired spectrum very flexibly. FIG. 4 shows an electronic circuit for controlling the LEDs. In the example shown, the control takes place via a CAN bus, with which 24 channels with respect to current flow and time behavior (pulse mode) can be programmed as desired.

In a second exemplary embodiment, a diffraction grating 5 is used as the spectrally selective component. Again, the spectrometer arrangement is used according to Figure 5 with reverse beam path. The emitted light of the spectral ordered according to their peak wavelength LED's 4 is coupled via the diffraction grating 5 to a large extent in an optical fiber or illumination optics. By using so-called imaging grating (English: "imaging grating"), it is possible to unite the LEDs in a "virtual source". Again, the LEDs 4 are controlled individually via current regulator. Advantage over the embodiment of Figure 3 is the larger aperture angle, which is detected by the entire system. Depending on the size of the diffraction grating 5 and the desired spectral splitting, a high collection efficiency can be achieved. Diffraction gratings 5 can nowadays be optimally adapted to the problem to be solved.

By individually controllable via current regulator LEDs, the spectral composition of the light arriving at the output of the optical fiber and / or illumination optics light can be influenced in a very effective manner. According to FIG. 2, in the spectral range between 370 nm and 960 nm, in principle, each wavelength can be generated by LEDs.

The multispectral illumination unit according to the invention is based on a spectrometer arrangement with a spectrometer crystal or a diffraction grating as the spectrally selective component which is operated with the reverse beam path. Instead of the photodetector is a linear array of LED's that emit light of different wavelengths and individually controlled by current regulator available.

With the arrangement according to the invention, a very compact, electronically spectrally controllable and almost arbitrarily switchable multispectral illumination unit is provided, which in principle can be used anywhere where spectrally controllable, homogeneous light sources are required. The lighting conditions can be changed very quickly and precisely.

Claims

claims

1. Multispectral illumination unit based on a Spektrometeranord- tion, in which instead of the photodetector a linear array of LEDs (4) emitting light of different wavelengths and individually controlled by current regulator is present, the LED's (4) according to their peak wavelength spectral are ordered, whose emitted light is coupled by a spectrally selective component in an optical fiber (1) and / or illumination optics and mixed in this, so that emerges at the output spectrally and laterally homogeneous light.

2. Multispectral illumination unit according to claim 1, in which a spectrometer crystal (2) or a diffraction grating (5) is used as the spectrally selective component.

3. Multispectral illumination unit according to at least one of claims 1 and 2, wherein the optical fiber (1) and / or illumination optics compared to a spectrometer arrangement has a larger diameter.

4. Multispectral illumination unit according to at least one of the preceding claims, in which by the individually controllable via current regulator LED's (4), the spectral composition of the light arriving at the output of the optical fiber and / or illumination optics can be influenced.