Dimmable lighting devices and methods for dimming same
In a single lighting device including a large number of light-emitting elements (LEEs), the LEEs are divided into separately powered groups, and different combinations of the groups are fully energized to achieve the desired overall brightness. In some embodiments, the number of LEEs in each group has a binary relationship to the other groups. The resolution of the dimming is the brightness of the smallest group. In one example of five binary weighted groups of LEEs, 32 brightness levels can be achieved while the LEEs in the energized groups are fully ON. Thus, since there is no high frequency switching, there is substantially no power dissipation by the dimming control system, and there is limited noise or EMI created. The dimming control can be easily implemented with a logic circuit controlling a transistor switch for each group.
1. A lighting device comprising:
one or more substrates including electrical conductors;
a plurality of groups of light-emitting elements (LEEs), each of the groups of LEEs comprising one or more LEEs disposed on the one or more substrates and in contact with the electrical conductors, the groups of LEEs being configured to provide a nominal light output when energized under nominal operating conditions, wherein the groups of LEEs are independently energizable and each of the nominal operating conditions associated with each of the groups of LEEs includes a corresponding nominal drive current; and
a dimming control system operatively connected to the groups of LEEs via the electrical conductors and configured to
determine a binary dimming code based on a dimming signal, the binary dimming code having a plurality of bits, each of the groups of LEEs associated with a corresponding bit of the dimming code, and
provide the corresponding nominal drive current to each of the groups of LEEs, based on the bit value of the corresponding bit of the dimming code, to respectively energize each of the groups of LEEs.
2. The lighting device according to claim 1 , wherein the dimming control system is further configured to infer operating conditions of one or more of the LEEs based on one or more drive currents provided by the dimming control system to one or more of the groups of LEEs and to control the drive current of each of the groups of LEEs based on the bit value of the corresponding bit of the dimming code, the inferred operating conditions and a predetermined association between light outputs and operating conditions of the groups of LEEs.
3. The lighting device according to claim 1 further comprising one or more sensors configured to provide an indication of one or more sensed operating conditions of one or more of the LEEs, wherein the dimming control system is further configured to control drive currents of each of the groups of LEEs based on the bit value of the corresponding bit of the dimming code, the sensed operating conditions, the nominal light outputs and the nominal operating conditions of the groups of LEEs.
4. The lighting device according to claim 1 , wherein different ones of the groups of LEEs provide different amounts of light at the corresponding nominal operating conditions.
5. The lighting device according to claim 1 , wherein different ones of the groups of LEEs provide different light-emission patterns at the corresponding nominal operating conditions.
6. The lighting device according to claim 1 , wherein the numbers of LEEs in two or more groups are integer powers of two scaled by a factor which is the same for the two or more groups.
7. The lighting device according to claim 6 , wherein the numbers of LEEs in the groups are integer powers of two.
8. The lighting device according to claim 1 , wherein the light output of each group corresponds with a difference in light outputs of the lighting device between adjacent dimming levels of the lighting device.
9. The lighting device according to claim 3 , wherein the one or more sensed operating conditions include one or more operating temperatures.
10. The lighting device according to claim 3 , wherein the one or more sensed operating conditions include one or more properties of light emitted by one or more of the LEEs.
11. The lighting device according to claim 10 , wherein the one or more properties of light include radiant flux.
12. The lighting device according to claim 10 , wherein the one or more properties of light include luminous flux.
13. The lighting device according to claim 10 , wherein the one or more properties of light include chromaticity.
14. The lighting device according to claim 1 , wherein the LEEs in one or more of the groups of LEEs are arranged pseudo randomly.
15. The lighting device according to claim 1 further comprising a homogenizer arranged to receive light from the groups of LEEs, the homogenizer configured to homogenize the light received from the groups of LEEs and to provide homogenized light, the homogenized light having a more homogenous appearance than the light received by the homogenizer from the groups of LEEs.
16. The lighting device according to claim 1 , wherein the LEEs are arranged to provide one or more of the nominal light outputs of the groups of LEEs with a first light-emission pattern and one or more of the nominal light outputs of the groups of LEEs with a second light-emission pattern different from the first light-emission pattern.
17. The lighting device according to claim 16 , wherein the first light-emission pattern is configured to provide illumination of an office space during operating hours and the second light-emission pattern is configured to provide illumination of the office space during closing hours.
18. The lighting device according to claim 16 , wherein the first light-emission pattern is configured to provide illumination of a space for task lighting and the second light-emission pattern is configured to provide illumination of the space for mood lighting.
19. The lighting device according to claim 1 , wherein the dimming control system is directly connected to the electrical conductors and is disposed adjacent to the one or more substrates.