DE102007022606B4 - Illumination system for imaging illumination with high homogeneity - Google Patents

Abstract

Illumination system for imaging illumination with a plurality of LEDs (1) with imaging optics (4), wherein the illumination system comprises a reflector (11) with a reflector contour and a focal point, wherein the LEDs (1) housed in the vicinity of the reflector contour and uniformly over the circumference the reflector are distributed, wherein in the focal point of the reflector (11) a compact scattering medium (14) is housed, wherein the light from the LEDs (1) by means of the imaging optics (4) is directed substantially to the scattering medium (14) and of is scattered there on the reflector contour, so that the reflector (11) leaving light is homogeneously emitted, characterized in that the reflector (11) is filled with a potting compound (15), wherein the scattering medium (14) in the potting compound (15 ) is placed, and being involved as a scattering medium small particles of higher refractive index plastic in a low-refractive potting compound.

Description

Technical area

The invention is based on an illumination system for imaging illumination for imaging illumination with high homogeneity according to the preamble of claim 1. Such illumination systems are of particular interest for use in stage construction or vehicle construction.

State of the art

The US Pat. No. 4,821,114 discloses an illumination optical system with filter wheel and white light source in the form of a lamp. Blocking filters such as absorption filters and dichroic filters are used. They are inserted into the beam path of almost punctiform light sources such as xenon high pressure discharge lamps. A continuous color change is thus possible only with multiple filter wheels and must be realized consuming by mechanical means. The filter wheels are placed behind each other and rotated appropriately. The control is complex and the filters are very expensive.

A controller for groups of LEDs is for example in US 5 515 136 A and US Pat. No. 6,630,801 B2 specified. In WO 2007/025525 A2 describes a module in which several highly efficient LEDs are combined on one board. These are then mapped to one point.

The publication US 2003/0117798 A1 discloses a luminaire with a reflector and a plurality of light-emitting diodes (LED), which are arranged in the vicinity of the reflector contour. At the focal point of the reflector, a compact scattering medium is arranged. The light of the LED is reflected by the reflector contour and radiated homogeneously forward through the scattering medium.

The publication US 2002/0024818 A1 discloses a headlamp for vehicles with a reflector, at least one LED and an at least partially reflective and / or scattering optical element. The light of the LED is radiated or deflected at least partially via this optical element.

The publication DE 696 22 820 T2 revealed in the 6 . 7 a lighting system with a concave support. In the carrier, a plurality of LEDs are arranged and aligned such that the light of each LED is focused by an aspheric condenser lens at the focal point F. A holographic diffuser is positioned at focus F and scatters the light focused thereon. As a result, a light decrease of individual LED in the image plane of a downstream cylindrical lens does not disturbing locally but only evenly distributed.

The publication US 5,966,393 A. discloses an illumination system in which the light from an LED is at least partially absorbed, wavelength converted, and re-emitted by a phosphor layer disposed near the LED.

The publication US 2001/0019487 A1 discloses a light guide in which one end is coupled by means of LED light. Along the light guide several spots are arranged to decouple the light transversely to the longitudinal axis of the light guide.

The publication US 2005/0105301 A1 discloses a light source with a reflector and a plurality of laser diodes. The laser diodes are arranged and aligned outside the reflector so that their light is focused through openings in the reflector in a focus. The focus is a phosphor arranged, which is supported by the inside of a reflector glass final disc. The phosphor is excited by the radiation of the laser diodes, wherein the light emitted by the phosphor light is reflected by the reflector and emitted to the outside.

The publication US 2005/0063185 A1 discloses an illumination system in which the light of a plurality of LEDs is focused into a concave reflector and enters a convex reflector inside. From the convex reflector, the light is emitted via the concave reflector to the outside.

The publication US 2002/0080614 A1 discloses an illumination system with a lamp and a reflector, wherein at least one prism for influencing the emission characteristic is arranged inside the reflector.

The publication US Pat. No. 6,193,383 B1 discloses an illumination system having a light source and an elongated light guide. Within the elongated optical waveguide, an inverted triangular-shaped opening is formed in the center in order to laterally deflect light rays coming from the light source.

Presentation of the invention

The object of the present invention is to provide a lighting system which ensures the imageability in a simple manner.

This object is achieved by the characterizing features of claim 1.

Particularly advantageous embodiments can be found in the dependent claims.

Imageable high-power LEDs are currently one of the biggest technical challenges. In addition to the generation of white light, in particular the realization of the imaging capability plays an important role. Previous approaches therefore provide the superimposed imaging of multiple LEDs. However, this approach has several disadvantages. A relatively complex system, which images several LEDs at the same time, is costly because the optics must be created multiple times.

An entirely different disadvantage of the known solutions is that white LEDs are used which are designed as conversion LEDs. This means that a phosphor layer partially or completely converts the primarily emitted light of the LEDs into longer-wave radiation. The phosphor is necessarily attached in the immediate vicinity of the chip. However, these phosphors are basically more or less temperature-sensitive. At junction temperatures beyond 150 ° C, all known phosphors show significant efficiency losses due to thermal quenching. Individual phosphors, which are good at room temperature, are even more sensitive. Overall, this results in reduced efficiency. There is no meaningful technical solution for this.

The novel solution finds a convincing way to realize the separation between light source and phosphor.

In particular, it is an illumination system for imaging illumination with at least one compact light source. This is an LED. In this case, the illumination system comprises a reflector with a reflector contour, wherein the light source is housed in the vicinity of the reflector contour, wherein at the focal point of the reflector, a compact scattering medium is housed, wherein the light from the light sources is directed substantially to the scattering medium and from there to the Reflector contour is scattered so that the light leaving the reflector is radiated homogeneous.

In particular, each light source consists of several groups of similar light sources. The light sources are LEDs. Frequently, at least three to seven similar light sources are used. If appropriate, these can also be arranged in groups which are controlled differently by different electronic means.

The light source is usually colored, especially blue emitting in the peak.

The illumination system preferably uses a compact scattering medium which has the shape of a sphere. The realization of the ball can be done by a drop. This drop can use a cast resin as a basic framework. The actual scattering agent in the scattering medium is an inert spreader, advantageously in the form of particles dispersed in casting resin. Particularly preferably, the scattering medium now additionally contains one or more phosphors for the conversion of the light emitted by the light source. In a simple embodiment, however, the light source itself may also be white and possibly already contain the phosphor itself. The light source is then a white LED.

The support of the scattering medium in the reflector is carried out by the reflector is filled with a potting compound, wherein the scattering medium is placed in the potting compound.

The scattering medium ultimately serves as a virtual light source in the reflector. Therefore, its volume should be as small as possible, in any case less than 50 mm ³ , preferably ≤ 10 mm ³ .

Brief description of the drawings

In the following, the invention will be explained in more detail with reference to several embodiments. The figures show:

1 the radiation characteristic of a normal LED;

2 the emission characteristic of a LED with microlens;

3 a lighting system with reflector in cross section;

4 a lighting system with reflector in cross section;

5 a reflector in plan view;

6 the beam path in the reflector;

7 a drop in detail

8th another embodiment of a lighting system;

9 different lens shapes.

Preferred embodiment of the invention

1 shows the cosine emission characteristic of a normal LED 1 , The Rays 2 diverge from the chip 3 off in all directions. The arrow length symbolizes the relative intensity.

2 shows an LED 1 with upstream microlens 4 as is known. This has the task, the light of the chip 3 to bundle. This makes it possible to image on a focal spot for a single LED.

3 shows in cross section a lighting system 10 with several LEDs 1 and with a reflector 11 , This one has a contour 12 which is parabolic, for example. In the wall of the reflector contour 12 sit several LEDs with imaging optics 4 , For example, a microlens. The reflector is with potting compound 13 , as known, filled. At the focal point of the reflector is as a scattering agent in the potting compound about 1 mm in diameter measuring drops 14 brought in.

The LEDs can also work in accordance with 4 Sitting outside of the reflector in a certain proximity, it requires in the reflector only one opening 21 to the light of an LED 1 until dripping 14 to lead. This allows easier installation because there are no longer any issues with cooling and adjusting the LEDs. In addition, the lossy area in the contour can be minimized.

The scattering drop consists of a highly concentrated mixture of potting compound 15 like epoxy resin and an inert spreader. For the realization of the inert spreader, the active droplet is realized as a plastic hybrid, ie small particles of higher refractive index plastic are incorporated into a low-pore casting compound.

Preferably, the scattering medium is spherical, but it may also have different shape in individual cases.

The scattering drop additionally contains phosphor particles 22 , please refer 7 such as YAG: Ce, nitrides, thiogallates, sulfides, Sione or orthosilicates or chlorosilicates, alone or in a suitable combination. The LED may also be a UV-emitting LED, but a blue LED is preferred because its radiation is less aggressive to the resin.

Preferably, the scattering medium is spherical, but it may also have different shape in individual cases. In the wall of the reflector groups of blue LEDs are embedded, which are each provided with microlenses for light extraction. Their optics are set so that the respective individual chip is imaged onto the scattering medium. The number of individual LEDs is ultimately limited only by the size of the reflector.

In order not to affect the efficiency of the reflector too much, the usable area of the reflector should not be restricted too much by the LEDs. An acceptable value is less than 20%, especially 1 to 5%.

The scattering drop scatters the light of all LEDs, with a suitable choice of the concentration of scattering particles, almost isotropic. In the end, the scattering drop then acts like a punctiform white or colored light source in the reflector.

For a colored light source, for example blue LEDs can be used, which are scattered only on a pure scattering medium.

The control of the LEDs is preferably carried out as a group. But it can also be done in different groups. This allows direct selection of any color locus as known per se for LEDs. There are many known methods, for example, as in the US Pat. No. 6,630,801 described.

5 shows a reflector 12 in plan view. The LEDs, here as examples as different groups 17 . 18 . 19 shown, which are controlled differently, are evenly distributed over the circumference of the reflector, so that the incidence of light on the drops is as homogeneous as possible. The LEDs are alternatively arranged so that they are evenly distributed in several rings over the circumference of the reflector. They thus ensure even better homogeneous illumination of the dross drop.

6 shows in cross-section how the light from the reflector 11 is emitted. Coming from the LEDs it is in the scattering drop 14 isotropically scattered and emitted. In front of the reflector, a condenser 20 sitting, who images the light on a point. Also possible is the coupling into a light guide.

Of course, a free-form reflector as known per se can be used, wherein the shape of the spill droplet then has no spherical shape, but rather has a different distortion, which is adapted to the reflector. the shape of the drop can also be optimized to realize a predetermined emission characteristic together with the reflector, as is desired, for example, in motor vehicle headlamps.

Claims (5)

Lighting system for imaging illumination with multiple LEDs ( 1 ) with imaging optics ( 4 ), wherein the illumination system is a reflector ( 11 ) with a reflector contour and a focal point, wherein the LEDs ( 1 ) are housed in the vicinity of the reflector contour and distributed uniformly over the circumference of the reflector, wherein at the focal point of the reflector ( 11 ) a compact scattering medium ( 14 ) is housed, with the light from the LEDs ( 1 ) by means of the imaging optics ( 4 ) essentially to the scattering medium ( 14 ) is directed and is scattered from there to the reflector contour, so that the reflector ( 11 ) emitted light is homogeneously emitted, characterized in that the reflector ( 11 ) with a potting compound ( 15 ), whereby the scattering medium ( 14 ) in the potting compound ( 15 ) is placed, and being involved as a scattering medium small particles of higher refractive index plastic in a low-refractive potting compound. Lighting system according to claim 1, characterized in that the LEDs ( 1 ) are themselves colored, and that the scattering medium ( 14 ) one or more phosphors for conversion of the LEDs ( 1 ) emitted light contains. Illumination system according to claim 1, characterized in that the compact scattering medium ( 14 ) has the shape of a sphere. Illumination system according to claim 2, characterized in that the LEDs ( 1 ) emit blue light emitted by the converting scattering medium ( 14 ) is converted so that the reflector ( 11 ) leaving light is white. Illumination system according to claim 1, characterized in that the volume of the compact scattering medium ( 14 ) is less than 50 mm ³ , preferably ≤ 10 mm ³ .

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