WO2011132110A1

WO2011132110A1 - Lighting device for variable beam spot illumination

Info

Publication number: WO2011132110A1
Application number: PCT/IB2011/051552
Authority: WO
Inventors: Frank Van Zon; Ralph Kurt; Ramon Pascal Van Gorkom; Mark Eduard Johan Sipkes
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-04-19
Filing date: 2011-04-12
Publication date: 2011-10-27

Abstract

Alighting device (10;30;40;50)for spot illumination comprising: a collimating optical element (15) having an entrance aperture(16), and an exit aperture(17) being larger than the entrance aperture(16); a light-source array(11) comprising a plurality of light-sources(12) arranged to emit light into the collimating optical element (15) at the entrance aperture(16) thereof; and at least one movably arranged light-shutter (18a-d) arranged at the exit aperture (17) of the collimating optical element (15). Through the provision of the collimating optical element, the correlation between the position at the output of the collimating optical element and the direction of the output light at the output of the collimating optical element can be improved.

Description

Lighting device for variable beam spot illumination

TECHNICAL FIELD

The present invention relates to a lighting device for spot illumination, comprising a light-source array. BACKGROUND OF THE INVENTION

In spot illumination applications, such as scene setting or other atmosphere creating lighting, high-power white light sources, such as halogen lamps, are widely used. To create light-beams of different colors, color filters are placed in front of the light-source, and to shape or control the light-beam, so-called "barn-doors" are often used. Barn doors are shutters that are arranged on different sides of the output of the lighting device (for example spot light). The shutters can be controlled to partly cut of the light-beam so as to control the spatial distribution of the light-beam.

Recent developments of high-power solid state light-sources, such as light- emitting diodes (LEDs) have contributed to an increase in the number of available lighting devices for spot illumination applications, which use an array of light-sources, such as LEDs. The use of an array of light-sources, such as LEDs, in a lighting device for spot illumination has important advantages, such as a reduced power consumption and a reduced heat radiation. However, developers of such lighting devices are still faced by several challenges, such as thermal control, mechanical housing and color binning.

Furthermore, it is desirable to provide the same functionalities for light-source array based lighting devices for spot illumination as are available for traditional lighting devices for spot illumination. One of those functionalities is the barn-door functionality discussed above.

In Fig. 1, an example of a LED-based lighting device that is currently available on the market is shown. The lighting device 1 comprises a large number of LEDs 2 (only one LED is indicated by a reference numeral in Fig. 1) arranged in a plane. The lighting device 1 further has four barn-doors 3a-d arranged as indicated in Fig. 1. When those barndoors 3a-d are operated, the lighting device 1 in Fig. 1 does not, however, produce the output that would be expected by a user who is used to conventional barn-door equipped lighting devices for spot illumination applications. In particular, operating the barn-doors 3a-d, would not result in the desired shaping of the light-beam, but in a light-beam having a reduced intensity, as well as various artifacts, such as multiple shadows (with a step-wise gradient). Furthermore, undesirable color effects occur at the edges of each shadow.

SUMMARY OF THE INVENTION

In view of the above, a general object of the present invention is to provide an improved lighting device for spot illumination, providing for an improved capability to vary the shape of the light-beam output by the lighting device.

According to the invention, there is provided a lighting device for spot illumination comprising: a collimating optical element having an entrance aperture, and an exit aperture being larger than the entrance aperture; a light-source array comprising a plurality of light-sources arranged to emit light into the collimating optical element at the entrance aperture thereof; and at least one movably arranged light-shutter arranged at the exit aperture of the collimating optical element in such a way that the light-shutter can be moved to partly block a light-beam output through the exit aperture of the collimating optical element to thereby shape the light-beam.

By "collimating optical element" should, in the context of the present application, be understood an optical element capable of collimating light, i.e. reducing the spatial spreading of light output by one or several light-source(s). The collimating optical element may be realized in the form of a single optical member, or may be comprised of several co-operating optical members.

The present invention is based on the realization that the problems encountered when trying to implement barn-door functionality in the prior art lighting device 1 shown in Fig. 1 are mainly caused by the fact that there is no correlation between the position at the output of the lighting device 1 and the direction of the light that is output by the lighting device. This behavior of the lighting device 1 in Fig. 1 is illustrated in Fig. 2, which is a simplified section view showing a single barn-door 3d being operated. As can be understood from Fig. 2, the spatial distribution of light output by the lighting device 1 when the barn-door 3d is operated is almost unchanged as compared to the case when all barndoors 3a-d are outside the light-beam as illustrated in Fig. 1. Based on this realization, the present inventors have further realized that the above-described problem can be at least partly solved by providing a collimating optical element between the light-sources 2 and the barndoors 3a-d. Through the provision of the collimating optical element, the correlation between the position at the output of the collimating optical element and the direction of the output light at the output of the collimating optical element can be improved.

Advantageously, the collimating optical element may be configured in such a way that a majority of light-rays output by the lighting device move away from an optical axis of the lighting device with increasing distance from the exit aperture of the collimating optical element, along the optical axis of the lighting device. That this is the case can, for example, be determined by photometric measurements of the radial light distribution (polar light diagram) at different positions at the exit aperture of the collimating optical element, preferably using a (small) diaphragm at the exit aperture of the lighting device for spot illumination. Such a collimating element may also be referred to as "a diverging collimating optical element".

Advantageously, the light-rays output by the lighting element may be continuously diverging after having passed through the exit aperture. In other words, a majority of the light-rays may not cross the optical axis after having passed through the exit aperture.

For a "perfect" barn-door functionality, all light-rays should preferably propagate in parallel with, or move away from the optical axis of the lighting device with increasing distance from the exit aperture of the collimating optical element. However, a substantial improvement as compared to the prior art lighting device 1 in Fig. 1 can be achieved if more than 70%, preferably more than 80%, most preferably more than 90% of the light-rays move away from the optical axis of the lighting device with increasing distance from the exit aperture of the collimating optical element.

With the lighting device according to various embodiments of the present invention, the desired barn-door functionality can be achieved, while still enjoying all the benefits provided by replacing traditional relatively inefficient light-sources with light- sources arrays, such as LED-arrays.

According to one embodiment, the collimating optical element may comprise a tubular reflector having the entrance aperture and the exit aperture; and a diverging optical element arranged to spread the light emitted by the light-sources.

Such a tubular reflector may be realized in various shapes. For example, the tubular reflector may exhibit rotational symmetry (about the optical axis), or the tubular reflector may have a polygonal cross-section in a plane perpendicular to the optical axis, as will be described further below. Moreover, the tubular reflector may exhibit any one of, or a combination of, various cross-sections in a plane including the optical axis, depending on the application. For example, this cross-section may be concave ("trumpet shaped"), convex (for example parabolic), or linear.

Accordingly, the tubular reflector may advantageously comprise a parabolic portion.

The diverging optical element may advantageously be a diffuser, which can co-operate with the tubular reflector to achieve the desired divergent collimation of the light output by the light-source array.

Advantageously, the optical diffuser may be arranged at a diffuser position located along the optical axis of the lighting device and at a distance from the entrance aperture of the tubular reflector, which is more than 20% and less than 80% of a distance from the entrance aperture to the exit aperture of the tubular reflector, along the optical axis of the lighting device.

By arranging the optical diffuser inside the tubular reflector and spaced apart from the entrance aperture and the exit aperture, a very attractive combination of sufficient color mixing, relatively narrow light-beam and improved barn-door functionality can be obtained.

Moreover, the tubular reflector may comprise a first portion providing a first divergence from the entrance aperture to the diffuser position and a second portion providing a second divergence greater than the first divergence from the diffuser position to the exit aperture. By the expression that a portion of the tubular reflector has a certain "divergence" should be understood that the portion of the tubular reflector is configured to collimate light to an emission cone having a certain opening angle. A greater divergence is equivalent to a larger opening angle of the emission cone.

Through this configuration of the tubular reflector, the light that is output by the light-sources can be "pre-focused" before it reaches the optical diffuser, to compensate for the broadening of the light-beam caused by the optical diffuser. After the light has passed through the optical diffuser, the light-beam is made divergent by the second portion of the tubular reflector to improve the correlation between the directions of the light-rays and their positions at the exit aperture of the tubular reflector. Hereby improved mixing of the light in combination with a further improved barn door functionality can be achieved. Advantageously, furthermore, the first portion of the tubular reflector may be defined by a parabola, and the second portion may be defined by a parabola that is tilted away from the optical axis of the lighting system.

Furthermore, at least a portion of the tubular reflector may have a substantially polygonal cross-section.

By "polygonal cross-section" should, in the context of the present application, be understood a cross-section that is bounded by a closed path of lines connected at at least three points, forming the corners of the polygonal cross-section. The lines can be straight or curved. For example, each path between the corners of the polygon may be concave or convex with respect to the polygonal cross-section. According to a preferred embodiment the polygonal cross section may be heptagonal (7 sides) or enneagonal (9 sides).

In the case where an optical diffuser is arranged at a diffuser position located along the optical axis of the lighting device and spaced apart from the entrance aperture and the exit aperture, the tubular reflector may advantageously have the above-mentioned polygonal cross-section in a portion located between the entrance aperture and the diffuser position, to enhance the mixing of light emitted by the different light-sources even further.

Moreover, the lighting device may comprise a plurality of movably arranged light-shutters arranged at the exit aperture of the collimating optical element. For example, the plurality of movably arranged light-shutters may be so-called "barn doors", which may be formed by flaps of metal or plastic or similar.

According to various embodiments of the present invention, the light-source array comprised in the lighting device may comprise a plurality of differently colored light- sources, which may advantageously be arranged in individually controllable sets of light- sources. Hereby, colored light can be achieved without using filters etc. Such differently colored light-sources may, for example, emit different primary colors or different whites, such as "warm white", "neutral white", or "cold white", etc.

Furthermore, such differently colored light-sources may advantageously be arranged in such a way that the colors are balanced (i.e. that the center of gravity for each color is in or close to the center of the light-source array).

Furthermore, the lighting device may additionally comprise a light-mixing arrangement arranged to mix the light emitted by the light-sources comprised in the light- source array, and to emit mixed light into the collimating optical element. Hereby, light- mixing can be even further improved, which contributes to reducing barn-door artifacts, such as colored edges. The light-mixing arrangement may advantageously comprise a (tubular) reflector having a polygonal cross-section to provide for good color mixing. In particular the polygonal cross section may be heptagonal (7 sides) or nonagonal / enneagonal (9 sides).

To provide for even further improved mixing of the light emitted by the light- sources, the light-mixing arrangement may further comprise an optically diffusing transmissive optical element arranged to diffuse light passing from the light-mixing arrangement into the collimating optical element.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an exemplary embodiment of the invention, wherein:

Fig. 1 illustrates a LED-based lighting device according to the prior art, being equipped with so-called barn doors;

Fig. 2 schematically illustrates why the desired shaping of light cannot be obtained using the prior art lighting device in Fig. 1;

Fig. 3a schematically illustrates a lighting device according to a first embodiment of the present invention;

Fig. 3b is a diagram illustrating the variation in spatial distribution of output light (barn-door effect) obtainable using the lighting device in Fig. 3a;

Fig. 4 schematically illustrates a lighting device according to a second embodiment of the present invention having a diverging optical element in the form of a negative lens arranged at the exit aperture of the collimating optical element;

Fig.5 schematically illustrates a lighting device according to a third embodiment of the present invention, comprising a light-mixing arrangement provided between the light-source array and the entrance aperture of the collimating optical element; and

Fig.6 schematically illustrates a lighting device according to a fourth embodiment of the present invention, comprising a tubular reflector with a polygonal cross- section.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Fig. 3 schematically illustrates an lighting device for spot illumination suitable for atmosphere creating lighting, such as scene setting. The lighting device 10 comprises a light-source array 11 formed by a plurality of light-sources 12 (only one of the light-sources is indicated by a reference numeral for ease of drawing), such as LEDs. The light-sources 12 are arranged on a carrier 13, which is in thermal contact with a heat-sink 14. The lighting device 10 further comprises a collimating optical element 15 having an entrance aperture 16 and an exit aperture 17. The light-source array 11 is arranged at the entrance aperture 16, and shutters 18a-c, so-called barn doors, are arranged at the exit aperture 17. The shutters 18a-c are provided in the form of flaps, which are movably arranged at the exit aperture 17 of the collimating optical element 15. By moving the flaps/barn doors 18a-c, the operator of the lighting device 10 can shape the beam by blocking light going in certain directions as will be described further below with reference to Fig. 3b.

As is schematically illustrated in Fig. 3a, the collimating optical element 15 comprises a tubular reflector 20, and a diverging optical element in the form of an optical diffuser 21. The optical diffuser 21 is arranged at a diffuser position between the entrance aperture 16 and the exit aperture 17, defining a first portion 23a of the tubular reflector 20 located between the entrance aperture 16 and the optical diffuser 21, and a second portion 23b of the tubular reflector 20 located between the optical diffuser 21 and the exit aperture 17. In the presently illustrated exemplary embodiment, the first portion 23a is substantially defined by a parabola, and the second portion 23b is defined by a parabola that is tilted away from an optical axis 25 of the lighting device 10.

By means of the optical diffuser 21, the light emitted by the light-sources is mixed and spread out, and through the divergent collimating properties of the second portion 23b of the tubular reflector, a relatively narrow light-beam can be formed, which still has a relatively strong correlation between the position at the output of the collimating optical element 15 and the direction of the light-rays at the exit aperture 17 of the collimating optical element 15.

Fig. 3b is a diagram illustrating the barn-door effect obtainable using the lighting device in Fig. 3a. The diagram in Fig. 3b shows the luminous intensity as a function of angular deviation from the optical axis in a plane including the optical axis.

In the diagram, three curves 27a-c are plotted, representing the angular distribution obtained using different configurations of the lighting device 10 in Fig. 3a.

With the barn doors 18a-c in the positions indicated in Fig. 3a, there is no shaping of the light-beam, which is illustrated by curve 27a in Fig. 3b. When one of the barn doors, say 18a, is moved into the light-beam, the light-beam is shaped, as is illustrated by curves 27b and 27c in Fig. 3b. Curve 27b illustrates the case without the optical diffuser 21, and curve 27c illustrates the case with the optical diffuser arranged as illustrated in Fig. 3a.

Various other embodiments of the lighting device according to the present invention will now be described with reference to Figs. 4-6.

Fig 4 is a schematic cross-section view of a lighting device 30, in which the optical collimating element 15 comprises a tubular reflector 20 and a diverging optical element in the form of a negative lens 31 arranged at the exit aperture 17 of the optical collimating element 15.

Fig 5 schematically illustrates a lighting device 40, comprising a collimating optical element 15 having an entrance aperture 16 and an exit aperture 17. At the exit aperture, barn doors 18a-d are movably arranged analogously as described above with reference to Fig. 3a. The lighting device 40 in Fig. 5 further comprises a light-mixing arrangement 41 arranged to mix the light emitted by differently colored light-sources (not visible in Fig. 5), and to emit the mixed light into the collimating optical element 15 at the entrance aperture 16. The light-mixing arrangement 41 may comprise a tubular reflector having a polygonal cross-section, and may also comprise an optical diffuser arranged to diffuse the light before it enters the collimating optical element 15. Hereby, improved color mixing can be obtained, which reduces various image artifacts, such as a colored border region at the edges of the light beam.

Finally, Fig. 6 schematically illustrates a lighting device 50 according to yet another embodiment of the present invention. As can be seen in Fig. 6, the collimating optical element 15 comprised in the lighting device 50 in Fig. 6 has a polygonal cross-section, and has segments 51 that extend along substantially straight lines from the entrance aperture 16 to the exit aperture 17 of the collimating optical element 15. Such a configuration provides for a very good mixing of the light emitted by the light-source array 11, which reduces various image artifacts, such as a colored border region at the edges of the light beam.

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. 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 lighting device (10; 30; 40; 50) for spot illumination comprising:

a collimating optical element (15) having an entrance aperture (16), and an exit aperture (17) being larger than the entrance aperture (16);

a light-source array (11) comprising a plurality of light-sources (12) arranged to emit light into the collimating optical element (15) at the entrance aperture (16) thereof; and

at least one movably arranged light-shutter (18a-d) arranged at said exit aperture (17) of the collimating optical element (15) in such a way that said light-shutter (18a-d) can be moved to partly block a light-beam output through said exit aperture (17) of the collimating optical element (15) to thereby shape said light-beam..

2. The lighting device (10; 30; 40; 50) according to claim 1, wherein said collimating optical element (15) is configured in such a way that a majority of light-rays output by the lighting device move away from an optical axis (25) of the lighting device with increasing distance from the exit aperture (17) of the collimating optical element (15).

3. The lighting device (10; 30; 40; 50) according to claim 2, wherein said collimating optical element (15) comprises:

a tubular reflector (20) having said entrance aperture (16) and said exit aperture (17); and

a diverging optical element (21; 31) arranged to spread the light emitted by said light-sources (12).

4. The lighting device according to claim 3, wherein said tubular reflector (20) comprises a parabolic portion (23a).

5. The lighting device according to claim 3 or 4, wherein said diverging optical element is an optical diffuser (21), preferably a holographic diffuser.

6. The lighting device according to claim 5, wherein said optical diffuser (21) is arranged between the entrance aperture (16) and the exit aperture (17) of said tubular reflector (20).

7. The lighting device according to claim 6, wherein said optical diffuser (21) is arranged at a diffuser position located along the optical axis (25) of the lighting device and at a distance from the entrance aperture (16) of the tubular reflector, which is more than 20% and less than 80% of a distance from the entrance aperture (16) to the exit aperture (17) of said tubular reflector, along said optical axis of the lighting device.

8. The lighting device according to claim 7, wherein said tubular reflector (20) comprises a first portion (23 a) having a first divergence from the entrance aperture (16) to the diffuser position and a second portion (23b) having a second divergence greater than said first divergence from the diffuser position to the exit aperture (17).

9. The lighting device according to claim 8, wherein said first portion (23 a) of the tubular reflector is defined by a parabola.

10. The lighting device according to claim 7 or 8, wherein said second portion (23b) of the tubular reflector is defined by a parabola that is tilted away from the optical axis

(25) of said lighting device.

11. The lighting device according to any one of claims 2 to 10, wherein at least a portion of said tubular reflector (20) has a substantially polygonal cross-section.

12. The lighting device according to any one of the preceding claims, comprising a plurality of movably arranged light-shutters (18a-d) arranged at said exit aperture (17) of the collimating optical element (15).

13. The lighting device according to any one of the preceding claims wherein said light-source array (11) comprises a plurality of differently colored light-sources, said lighting device further comprising a light-mixing arrangement (41) arranged to mix the light emitted by the light-sources (12) comprised in the light-source array, and to emit mixed light into said collimating optical element (15).

14. The lighting device according to claim 13, wherein said light-mixing arrangement (41) comprises a reflector having a polygonal cross-section.

15. The lighting device according to claim 13 or 14, wherein said light-mixing arrangement (41) further comprises an optically diffusing transmissive optical element arranged to diffuse light passing from said light-mixing arrangement into said collimating optical element (15).