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EP-4735791-A1 - LIGHTING DEVICE

EP4735791A1EP 4735791 A1EP4735791 A1EP 4735791A1EP-4735791-A1

Abstract

In an aspect, there is provided a lighting device (10) comprising: a light mixing chamber (12) comprising a reflective inner surface (12a) and a diffusive light exit window (20); a plurality of first LEDs (22) arranged in the light mixing chamber (12) on a bottom portion (14) thereof, wherein the plurality of first LEDs is configured to emit first light,; and at least one second LED (24) arranged in the light mixing chamber (12), wherein the at least one second LED is configured to emit second light; wherein the lighting device (10) is configured to emit a mixture of light through the diffusive light exit window (20), wherein the mixture of light comprises the first light emitted from the plurality of first LEDs (22) and the second light emitted from the at least one second LED (24); wherein at least a majority of the first light emitted from the plurality of first LEDs (22) defines directly propagating first light propagating directly to the diffusive light exit window (20), and the second light emitted from the at least one second LED (24) is propagating directly and/or indirectly to the diffusive light exit window (20); and wherein the at least one second LED (24) is arranged such that an average optical path length (L2) for the second light, between the at least one second LED (24) and the diffusive light exit window (20), exceeds an average optical path length (L1) for the directly propagating first light, between the first LEDs (22) and the diffusive light exit window (20).

Inventors

  • VAN BOMMEL, TIES

Assignees

  • Signify Holding B.V.

Dates

Publication Date
20260506
Application Date
20240624

Claims (14)

  1. 1. A lighting device (10) comprising: a light mixing chamber (12) comprising a reflective inner surface (12a) and a diffusive light exit window (20); a plurality of first LEDs (22) arranged in the light mixing chamber (12) on a bottom portion (14) thereof, wherein the plurality of first LEDs is configured to emit first light, and wherein each LED of the first LEDs comprises a first die (221) having a first surface area, SAI, wherein the first surface area SAI has a first largest spatial extent, SEI, that is less than or equal to 100 micrometers; and at least one second LED (24) arranged in the light mixing chamber (12), wherein the at least one second LED is configured to emit second light, and wherein each LED of the at least one second LED comprises a second die (241) having a second surface area, SA2, wherein the second surface area SA2 has a second largest spatial extent, SE2, that is greater than or equal to 300 micrometers; wherein a ratio, R, defined by SA2/SA1 is equal to or larger than 10; wherein the lighting device (10) is configured to emit a mixture of light through the diffusive light exit window (20), wherein the mixture of light comprises the first light emitted from the plurality of first LEDs (22) and the second light emitted from the at least one second LED (24); wherein at least a majority of the first light emitted from the plurality of first LEDs (22) defines directly propagating first light propagating directly to the diffusive light exit window (20), and the second light emitted from the at least one second LED (24) is propagating directly and/or indirectly to the diffusive light exit window (20); wherein the at least one second LED (24) is arranged such that an average optical path length (L2) for the second light, between the at least one second LED (24) and the diffusive light exit window (20), exceeds an average optical path length (LI) for the directly propagating first light, between the first LEDs (22) and the diffusive light exit window (20), and wherein a respective first die of each LED of the plurality of first LEDs (22) face the diffusive light exit window (20) and a respective second die of each LED of the at least one second LED (24) is arranged at an angle 0 different from zero with respect to the first dies, wherein preferably 0 is approximately 90 degrees and/or 180 degrees.
  2. 2. The lighting device (10) according to claim 1, wherein the average optical path length for the second light (L2) is at least 1.5 times greater than the average optical path length for the first light (LI).
  3. 3. The lighting device (10; 110) according to claim 1 or 2, wherein the at least one second LED (24) is arranged in the light mixing chamber (12) such that at least a majority of the second light emitted from the at least one second LED (24) propagates to the diffusive light exit window (20) via the reflective inner surface (12a) of the light mixing chamber (12).
  4. 4. The lighting device (10; 110) according to any one of the preceding claims, wherein the light mixing chamber (12) comprises a top portion (18) at least partly surrounding the diffusive light exit window (20) and facing the bottom portion (14), and a circumferential sidewall structure (16) extending between the bottom portion (14) and the top portion (18), and wherein the at least one second LED (24) is arranged on the sidewall structure (16) or on the top portion (18).
  5. 5. The lighting device (10) according to any one of claims 3-4, wherein: the diffusive light exit window (20) is substantially planar and substantially parallel to the bottom portion (14); and the aspect ratio of a width (W) and a height (H) of the light mixing chamber (12) is at least 8.
  6. 6. The lighting device (210; 310) according to any one of claims 1-2, wherein the at least one second LED (24) is arranged on the bottom portion (14) of the light mixing chamber (212; 312) and wherein a shape of the diffusive light exit window (220; 320) is such that a separation between each second LED (24) of the at least one second LED (24) and the diffusive light exit window (220; 320) exceeds a separation between each first LED (22) and the diffusive light exit window (220; 320).
  7. 7. The lighting device (210) according to claim 6, wherein the plurality of first LEDs (22) is arranged on a central portion (14a) of the bottom portion (14) and the at least one second LED (24) is arranged on a peripheral portion (14b) of the bottom portion (14b), and wherein the shape of the diffusive light exit window (220) is such that a height of the diffusive light exit window (220) above the bottom portion (14) is greater at the peripheral portion (14b) than the central portion (14a).
  8. 8. The lighting device (210) according to claim 7, wherein the light mixing chamber (212) comprises a circumferential sidewall structure (16) extending between the bottom portion (14) and the diffusive light exit window (220).
  9. 9. The lighting device (310) according to claim 8, wherein the at least one second LED (24) is arranged on a central portion (14a) of the bottom portion (14) and the plurality of first LEDs (22) is arranged on a peripheral portion (14b) of the bottom portion (14b), and wherein the shape of the diffusive light exit window (320) is such that a height of the diffusive light exit window (320) above the bottom portion (14) is greater at the central portion (14a) than the peripheral portion (14b).
  10. 10. The lighting device (310) according to claim 9, wherein the diffusive light exit window (320) is curved and defines an apex located above the central portion (14a).
  11. 11. The lighting device (10; 110; 210; 310) according to any one of the preceding claims, wherein a reflectivity of the diffusive light exit window is 28% or less, such as in a range from 15 to 25 %.
  12. 12. The lighting device (10; 110; 210; 310) according to any one of the preceding claims, wherein: the reflectivity of the reflective inner surface (14a; 212a; 312a) of the light mixing chamber (12; 212; 312) is at least 80%; and the absorbance of the diffusive light exit window for the first and second light is at most 2%.
  13. 13. The lighting device (10) according to any one of the preceding claims, wherein the lighting device (10) comprises a plurality of second LEDs (24), wherein the plurality of first LEDs are arranged at an average first pitch (Pl); the plurality of second LEDs are arranged at an average second pitch (P2); and wherein P2>2 P 1.
  14. 14. A luminaire comprising the lighting device (10, 110, 210, 310) according to any one of the preceding claims.

Description

LIGHTING DEVICE FIELD OF THE INVENTION The present invention generally relates to a lighting device. BACKGROUND OF THE INVENTION A light mixing chamber is a chamber or cavity, for instance box-shaped, with a reflective inner surface and a diffusive light exit window. Light mixing chambers are used in lighting applications for mixing light emitted by one or more light sources, typically light emitting diodes (LEDs), and thus provide a diffuse and even light output distribution. In many LED-based lighting applications it is desirable to have a light mixing chamber which has a low profile (i.e. being shallow), provides a homogeneous light distribution at its light exit window (e.g. without any appreciable LED spottiness), yet has a high output efficiency. However, while a high output efficiency may be provided using a diffusive light exit window with low reflectivity, this tends to reduce the homogeneity of the light distribution (e.g. an increased appearance of LED spottiness). Simultaneously addressing the above stated aims is hence not trivial. US 2010/290208 discloses a lighting device comprising a first group of solid state light emitters, an element containing luminescent material and a second group of solid state light emitters spaced from the element. In some embodiments, (1) at least 50 percent of light emitted by one of the first group does not mix with light emitted by the second group before the light emitted by the second group has entered the element, (2) at least 90 percent of exiting light emitted by the second group travels farther within the lighting device than 90 percent of exiting light emitted by the first group, (3) an average distance traveled by exiting light emitted by the second group is farther than an average distance traveled by exiting light emitted by the second group, and/or (4) light emitted by the first group directly exiting the lighting device exits the lighting device without being incident upon the element. WO 2008/135927 discloses a solid-state lighting device includes a plurality of light-emitting elements configured for generating light that are thermally coupled to a heat spreading chassis configured for coupling to one or more heat sinks. The lighting device further includes a mixing chamber which is optically coupled to the plurality of light-emitting elements and configured to mix the light emitted by the plurality of light-emitting elements. A control system is operatively coupled to the plurality of light-emitting elements, and configured to control operation of the plurality of light-emitting elements. SUMMARY OF THE INVENTION It is an object of the present invention to provide a lighting device comprising a light mixing chamber which may have a low profile, yet still enabling a homogeneous light distribution at its light exit window and a high output efficiency. These and other objects may be achieved by a lighting device in accordance with the independent claim. Embodiments of the present invention are defined in the dependent claims. Hence, according to an aspect of the present invention, there is provided a lighting device comprising: a light mixing chamber comprising a reflective inner surface and a diffusive light exit window; a plurality of first LEDs arranged in the light mixing chamber on a bottom portion thereof, wherein the plurality of first LEDs is configured to emit first light, and wherein each LED of the first LEDs comprises a first die having a first surface area, SAI, wherein the first surface area SAI has a first largest spatial extent, SEI, that is less than or equal to 100 micrometers; and at least one second LED arranged in the light mixing chamber, wherein the at least one second LED is configured to emit second light, and wherein each LED of the at least one second LED comprises a second die having a second surface area, SA2, wherein the second surface area SA2 has a second largest spatial extent, SE2, that is greater than or equal to 300 micrometers; wherein a ratio, R, defined by SA2/SA1 is equal to or larger than 10; wherein the lighting device is configured to emit a mixture of light through the diffusive light exit window, wherein the mixture of light comprises the first light emitted from the plurality of first LEDs and the second light emitted from the at least one second LED; wherein at least a majority of the first light emitted from the plurality of first LEDs defines directly propagating first light propagating directly to the diffusive light exit window, and the second light emitted from the at least one second LED is propagating directly and/or indirectly to the diffusive light exit window; and wherein the at least one second LED is arranged such that an optical path length for the second light (e.g. an average optical path length for the second light), between the at least one second LED and the diffusive light exit window, exceeds an optical path length for the directly propagating first light (e.g. an average optical