WO2011117815A1

WO2011117815A1 - Spot illumination system with improved light mixing

Info

Publication number: WO2011117815A1
Application number: PCT/IB2011/051197
Authority: WO
Inventors: Ralph Kurt; Teunis Willem Tukker
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-03-25
Filing date: 2011-03-22
Publication date: 2011-09-29
Also published as: TW201200802A

Abstract

A spot illumination system (10) comprising a collimating element (2) formed by a set of N funnel shaped reflectors (11) and a set of N light source arrays(1), each comprising a plurality of light sources (12). The reflectors each have a reflecting inner surface, an entrance aperture and an exit aperture, and are arranged in a bundle with all entrance apertures in one end and all exit apertures in an opposite end. The funnel shaped reflectors are further truncated so that a side (12) of a reflector facing an adjacent reflector terminates before the opposite end, such that the collimating element has N entrance apertures (7) leading into N funnel shaped reflectors (11), which funnel shaped reflectors merge into one single exit aperture(8). The N light source arrays(1) and arranged to emit light into one of the entrance apertures(7), respectively. The light from each light array is initially guided and mixed by a separate funnel shaped reflector, and then mixed with light from the other light arrays. As a result, an improved mixing and collimation is achieved compared to arranging N funnel shaped reflectors next to each other, and emitting light from N exit apertures.

Description

Spot illumination system with improved light mixing

FIELD OF THE INVENTION

The present invention relates to a spot illumination system, where light from a plurality of light sources is collimated to achieve a high power spot illumination. BACKGROUND OF THE INVENTION

In spot illumination applications, such as scene setting or other atmosphere creating lighting, white light sources with colored filters has been used to a great extent. Lately, as an alternative, illumination systems with colored light sources, such as light emitting diodes, LEDs, have been developed.

Using colored light sources eliminates the need for filtering, and thus increases efficiency and color consistency (replaced filter might introduce variation). Further, the emitted color can be changed by electronic control, and all accessible colors are always available without any hardware replacements. The market for these systems is quickly growing as LED performance improves.

In spot illumination applications, the homogeneity of the emitted light is of great importance. One example of an illumination system for spot illumination is described in US 6,200,002, wherein a tubular collimator collimates light from a light source array arranged in the collimator entrance.

Multi channel, high flux applications such as CDM replacement spots and multicolor entertainment spots (for theater/touring/stage/studio), require high light output.

Some applications like touring (temporary installations such as pop concerts and the like) and architectural, outdoor and street lighting light output in the range of about 10-50 klm. To achieve light output in this order, a large number of point light sources (e.g. LEDs) are needed and they have to be packed on a small array in a robust way. The performance of an assembly of individual LED packages is often limited. On the other hand dedicated very large LED arrays have intrinsically a low yield and they are too expensive for many applications. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a spot illumination system with sufficient light output having satisfactory color mixing and collimation, which can be manufactured /assembled with high yield.

This and other objects are achieved by a spot illumination system comprising a collimating element and a set of N light source arrays each comprising a plurality of light sources. The collimating element is formed by a set of N funnel shaped reflectors each having a reflecting inner surface, an entrance aperture and an exit aperture, the exit aperture being greater than the entrance aperture, the funnel shaped reflectors being arranged in a bundle with all entrance apertures in one end and all exit apertures in an opposite end, and wherein the funnel shaped reflectors are truncated so that a side of a reflector facing an adjacent reflector terminates before the opposite end, such that the collimating element has N entrance apertures leading into N funnel shaped reflectors, which funnel shaped reflectors merge into one single exit aperture. The N light source arrays are arranged to emit light into one of the entrance apertures, respectively.

The collimating element according to the invention thus receives light from N light sources and combines it into one light beam emitted from the single exit aperture. The light from each light array is initially guided and mixed by a separate funnel shaped reflector, and then mixed with light from the other light arrays. As a result, an improved mixing and collimation is achieved compared to arranging N funnel shaped reflectors next to each other, and emitting light from N exit apertures.

The collimating element according to the present invention further seamlessly combines N individual beams into one beam without visible borders between the individual beams.

The N light source arrays are preferably substantially identical. This provides an efficient manufacturing process, and enables optimal efficiency of the collimating element.

Each substantially identical light source array may be rotated around an optical axis in such a way as to avoid symmetry. By avoiding symmetry, the collimation and light mixing, is further improved. In the present context, a symmetric arrangement of light source arrays would imply that the relative rotation of each array corresponds to the number of arrays. For example, if N=3, then the relative rotation between arrays should not be 120 degrees in order to avoid symmetry. The truncated funnel shape reflectors are preferably arranged so closely together that the single exit aperture is smaller, most preferably 10%-20% smaller, than a combination of exit apertures of N non-truncated funnel shaped reflectors. Such a design further enhances collimation and light mixing.

A distance between adjacent light source arrays is preferably between 0.5 and 2 times an effective diameter of a light source array. According to one embodiment, the distance between adjacent light source arrays is approximately equal to the effective diameter of a light source array. Such a distribution of light source arrays (and thus entrance apertures of the collimating element) has shown to provide satisfactory collimation and mixing.

An effective diameter of the single exit aperture is preferably 1.5 - 6 times greater than an effective diameter of one light source array multiplied by N. This means that a beam width of the light emitted from each light source arrays is allowed to become 1.5 -6 times broader when passing the collimation element.

Each light-source array can comprise at least one set of light-sources configured to emit light of a first color and at least one set of light-sources configured to emit light of a second color different from the first color. By having multiple colors in each light source array, the spot illumination system may be controlled to emit a variety of colors.

The light mixing of the collimating element of the present invention will in this case include color mixing. Achieving color mixing inside the optics is efficient, compared to color mixing in the far field e.g. on a wall. A collimating element according to the invention can achieve an optical efficiency of more than 70%, which is challenging to reach in a collimating and mixing optics with high brightness.

In this context, a set of light-sources may be a single light-source, or may be a group of light-sources arranged together. For example, a set of light-sources may be provided in the form of a line of light sources in a 2D array.

The number N can be any number greater than 1. However, in currently considered embodiments, the number N belongs to the set [2, 3, 4, 5, 7, 9, 12]. It has been shown that with such a number N, the funnel reflectors can be interlaced to provide satisfactory light mixing.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of an illumination system according to an embodiment of the present invention.

Figure 2 shows the collimating element in figure 1 in more detail. Figure 3 is a plane view of the light emitting devices in the illumination system in figure 1.

Figure 4a-b are schematic plane views of collimating elements formed by three heptagonal interlaced tubular reflectors.

Figure 5 is a simulated beam profile of the collimating element in figure 4a.

Figure 6 is a schematic cross section of a collimating element formed by two heptagonal interlaced tubular reflectors.

Figure 7a-b are schematic cross sections of collimating elements formed by four heptagonal interlaced tubular reflectors.

Figure 8 is a schematic cross section of a collimating element formed by five octagonal interlaced tubular reflectors.

Figure 9 is a schematic cross section of a collimating element formed by seven octagonal interlaced tubular reflectors.

DETAILED DESCRIPTION OF Embodiments

Figure 1 shows a perspective exploded view of an illumination system for spot illumination suitable for atmosphere creating lighting, such as scene setting. The illumination system 10 here comprises three light source arrays 1, such as LED arrays, mounted on a carrier, such as a printed circuit board (PCB) 3, which is arranged on a heat spreader 4, which is in turn arranged on a heat sink 5. The illumination system 10 further comprises a collimating element 2 with a reflective inner surface. The collimating element has three entrance apertures 7, each aligned with one of the light source arrays 1, and only one exit aperture 8. At the exit aperture 8 of the collimating element 2, a diffusing member, here in the form of an optically diffusing sheet 9 is provided and or a field lens that further collimates the light beam.

The system 10 further comprises circuitry to power and control the light source arrays, but as this circuitry is not essential for the disclosure of the present invention, a description thereof has been omitted for sake of brevity.

A spacer ring 14 may serve as mechanical and optical interface between light source arrays and the collimating element.

The collimating element 2, which is shown in more detail in figure 2, has a shape corresponding to three funnel shaped, tubular reflectors 11, which have been interlaced with each other. Each tubular reflector here has a polygonal cross section in a plane perpendicular to the optic axis of the illumination system, in the illustrated case with seven sides (a heptagonal cross section). Sides 12 that meet sides of adjacent reflectors have been truncated to terminate before the end of the collimating element. Thereby, the three reflectors merge into one exit aperture 8. The entrance apertures 7a, 7b, 7c of the reflectors each form one of the entrance apertures of the collimating element 2.

The optical axis of the individual reflectors 11 can be slightly tilted towards the optical axis of the entire illumination system. This may further improve the combination of light beams from the individual light source arrays into one beam.

In figure 2, the reflective inner surfaces of the reflectors 1 la-c are straight. However, the inner surfaces may also be convex as seen from the optical axis of each entrance aperture, i.e. forming a trumpet shaped reflector. It may also be possible to have concave inner surfaces.

The body of the collimating element can be fabricated from polymeric material by assembling multiple pieces together or as a single piece e.g. by injection molding or rapid prototyping. A highly reflective foil such as Miro foil can then be attached (e.g. glued) onto the inner surface thereof. Alternatively, the inner surface can be coated with a high reflecting mirror. The reflective part of the envelope can be relatively thin with a thickness between 0.5mm and 10mm, preferably between 0.7mm and 5mm, most preferably between 0.8 and 2mm. The reflective part can be in contact with the heat spreader 4 or heat sink 5, and preferably it is attached to the board 3 on which the light source arrays 1 are mounted. Optionally, a POC foil is arranged at or close to the exit aperture 8 of the collimating element.

It is noted that the illumination system may generally comprise any number N of substantially identical light source arrays 1 and corresponding number of funnel shaped reflectors interlaced to form a collimating element 2 with one exit aperture 8. For example, N could be 2, 3, 4, 5, 7, 9 or 12, and some examples will be given in the following. The polygonal cross section may have any number of sides, such as four, five, six, seven, eight or nine. Alternatively, the cross section is not polygonal at all, but may be circular or elliptical.

Figure 3 illustrates the light source arrays 1 and their placement in more detail. Each array 1 is here substantially identical and comprises a plurality of light emitting devices 13, such as LEDs. The light source arrays 1 may comprise between 5 and 250 light sources, and typically between 70 and 150. A high densely packed LED array may have a high EPI density, preferably between 5 and 70%, more preferably between 15 and 50%.

Each array may further comprise several, for example 2-8, sets of light sources that emit different colors, for example one set of red LEDs, one set of blue LEDs, and one set of green LEDs. According to another example, the light source arrays include LEDs with white (W), red (R), green (G), blue (B) or amber (A), cyan (C), deep red (dR) and/or deep blue (dB) emission spectrum. By combination thereof, any desired light spectrum is obtainable that falls within the color space made up by the color coordinates of the

WRGBAdRdB starting LEDs. Other combinations are also possible, such as neutral white and warm white (NW + WW), combinations with cold white (e.g. CW + WW), (RGBA), (RGB AW), (RGBW), (RGB AC), (RGBAdR), (RGBACdR) and (RGBACdRW).

The light source arrays may be rotated relative each other, so as to avoid symmetry. For example, in the illustrated case with three light source arrays 1 , the light source arrays 1 should be rotated by an angle different from 120 degrees.

The lumen output of each light source array may be in the order of 1-10 klm, and the combined lumen output of the illumination system may be 40klm or greater, by combining several light source arrays.

The distance L between adjacent light source arrays may be between 0.5 and 2 times the effective diameter D of an LED array, and in the give example this distance L is approximately 0.8 D.

Figure 4a and 4b illustrates how different collimating elements may be formed using identical funnel shaped reflectors, simply by interlacing them with different distances L. In figure 4a, the reflectors 11 have been placed closer together than in figure 4b.

To illustrate the performance, figure 5 shows a simulation of the beam shaping function of the collimating element 2 in figure 2. It is clear that the collimating element can transform a Lambertian light distribution from light sources such as LEDs into the required beam shape of 10° - 40° FWHM.

In the case of multi-colored light source arrays 1, the collimating element should further provide satisfactory color mixing, i.e. it is a collimating and mixing element 2.

In order to realize a robust product, it is preferred to apply a transparent protection layer on top of the light source arrays or at least parts of them. The components (e.g. LEDs) and wire bonds to the circuitry are then protected against moisture,

contamination and unintended damage. This can be realized by suspension of silicon (like glob top), by over molding or under fill techniques.

A transmissive part may further be arranged directly on top of each light source array 1. It could be a single lens or curved surface, or be part comprising multiple lenses, microstructures or planar elements. Such a transmissive part may comprise a transmissive ceramic material, a substantially transmissive glass or polymeric foil material. The transmissive part may further comprise a transmissive silicon layer, which is direct contact with said LED array, for improved optical light out-coupling. The transmissive part may also comprise optical structure(s) with lens shape on the surface such as a microlens array.

To further improve the homogeneity of the light output by the illumination system, while keeping the reduction in output efficiency at a minimum, the illumination system 10 may advantageously comprise an optically diffusing member 9 arranged at the exit aperture 8 of the tubular reflector 2. Since the light is generally relatively homogeneous close to the optic axis, the light-diffusing member 9 has a lower diffusing capability there than further away from the optic axis. This may, for example be achieved by providing a film comprising scattering particles, where the concentration of scattering particles increases with increasing distance from the optic axis of the illumination system 10. The optically diffusing member 9 may, alternatively, have a hole in the middle and thus not absorb or scatter any of the light output by the illumination system 10 close to the optic axis thereof. As an alternative or complement to the scattering particles, the diffusing capability of the optically diffusing member 9 may be accomplished using other means, such as through a holographic pattern and/or a surface relief. It should be noted that the light-diffusing member 9 may

advantageously be made of a polymeric material.

Figure 6 shows a cross section of a collimating element formed by interlacing only two tubular reflectors.

Figures 7a and 7b show two different examples of cross sections of collimating elements formed by interlacing four heptagonal tubular reflectors. In figure 6a, the distance between the tubular reflectors is smaller than in figure 6b.

Figure 8 shows an example of a cross section of a collimating element formed by interlacing five octagonal tubular reflectors.

Figure 9 shows an example of a cross section of a collimating element formed by interlacing collimating element with seven octagonal tubular reflectors.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. For example, other dimensions and/or relations between dimensions may be employed. Also, other geometries than the ones disclosed may be applied. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

CLAIMS:

1. A spot illumination system (10) comprising:

a collimating element (2) formed by a set of N funnel shaped reflectors (11) each having a reflecting inner surface, an entrance aperture and an exit aperture, said exit aperture being greater than said entrance aperture, said funnel shaped reflectors being arranged in a bundle with all entrance apertures in one end and all exit apertures in an opposite end, and wherein said funnel shaped reflectors are truncated so that a side (12) of a reflector facing an adjacent reflector terminates before said opposite end, such that said collimating element has N entrance apertures (7) leading into N funnel shaped reflectors (11), which funnel shaped reflectors merge into one single exit aperture (8), and

a set of N light source arrays (1), each comprising a plurality of light sources

(12) and arranged to emit light into one of said entrance apertures (7), respectively.

2. The spot illumination system according to claim 1, wherein the N light source arrays (1) are substantially identical.

3. The spot illumination system according to claim 2, wherein each of the N substantially identical light source arrays is rotated around an optical axis in such a way as to avoid symmetry.

4. The spot illumination system according to any one of the preceding claims, wherein said single exit aperture (8) is smaller than a combination of exit apertures of N non- truncated funnel shaped reflectors.

5. The spot illumination system according to claim 4, wherein said single exit aperture (8) is 10% - 200% smaller than a combination of exit apertures of N funnel shaped reflectors.

6. The spot illumination system according any one of the preceding claims, wherein a distance (L) between adjacent light source arrays (1) is between 0.5 and 2 times an effective diameter (D) of a light source array (1).

7. The spot illumination system according to claim 6, wherein the distance (L) between adjacent light source arrays (1) is approximately equal to the effective diameter (D) of a light source array.

8. The spot illumination system according to any one of the preceding claims, wherein an effective diameter of said single exit aperture (8) is 1.5 - 6 times greater than an effective diameter (D) of one light source array multiplied by N.

9. The spot illumination system according to any one of the preceding claims, wherein each truncated funnel shaped reflector has a polygonal cross-section.

10. The illumination system according to any one of the preceding claims, wherein each light-source array (1) comprises at least one set of light-sources configured to emit light of a first color and at least one set of light-sources configured to emit light of a second color different from the first color.

11. The spot illumination system according to any one of the preceding claims, wherein N belongs to the set [2, 3, 4, 5, 7, 9, 12].