Lifetime color stabilization of color-shifting artificial light sources
A system includes two or more phosphor-containing white LEDs (or other color-shifting artificial light sources) selected so that their combined color shift over at least 8,000 hours (e.g., at least 10,000 hours, at least 20,000 hours, at least 30,000 hours, at least 40,000 hours, up to 200,000 hours, up to 100,000 hours, up to 80,000 hours) of operation is less than at least one of the LED's (or the other color-shifting artificial light source's) color shift over that time. Here, the combined color shift (Δu′v′) over the at least 8,000 hours (e.g., at least 10,000 hours, at least 20,000 hours, at least 30,000 hours, at least 40,000 hours, up to 200,000 hours, up to 100,000 hours, up to 80,000 hours) of operation can be less than 0.007 (e.g., 0.006 or less, 0.005 or less, 0.004 or less, 0.003 or less, 0.002 or less, 0.001 or less, 0.0005 or less).
1 . A system, comprising:
two or more phosphor-containing white LEDs configured to emit white light during operation of the system, each of the white LEDs having a corresponding predetermined color shift over a period of operation of the system,
wherein the white light emitted by the two or more LEDs combined has a combined color shift (Δu′v′), over the period of operation of the system, that is both less than 0.007 and less than at least one of the LEDs' color shifts,
the period of operation being a predetermined number of hours that commences after 1,000 hours or more of operation of the system and before 200,000 hours of operation of the system.
2 . The system of claim 1 , wherein the predetermined number of hours is 8,000 hours.
3 . The system of claim 1 , wherein the combined color shift (Δu′v′) over the operating time is less than 0.006.
4 . The system of claim 1 , wherein the system is a light bulb comprising the two or more phosphor-containing white LEDs.
5 . The system of claim 1 , wherein the system is a luminaire comprising the two or more phosphor-containing white LEDs.
6 . The system of claim 1 , comprising multiple bulbs and/or luminaires which include the two or more phosphor-containing white LEDs.
7 . The system of claim 1 , comprising a current varying module configured to selectively vary a relative current to each of the two or more phosphor-containing white LEDs in order to vary their relative brightness.
8 . The system of claim 7 , wherein the current varying module comprises a feedback loop or a feedforward loop based on which the current varying module varies the relative current to each of the two or more phosphor-containing white LEDs.
9 . The system of claim 8 , wherein the feedback loop comprises at least one sensor associated with the two or more phosphor-containing white LEDs, the at least one sensor configured to produce feedback information based on which the feedback loop is operated.
10 . The system of claim 9 , wherein the at least one sensor comprises a current sensor.
11 . The system of claim 10 , wherein the at least one sensor comprises a spectral sensor.
12 . The system of claim 9 , wherein the at least one sensor comprises a temperature sensor.
13 . The system of claim 1 , wherein the two or more phosphor-containing white LEDs are combined based on a predicted color shift for each of the LEDs.
14 . The system of claim 13 , wherein the color shift is predicted based on a measurement of the two or more phosphor-containing white LEDs' actual color shifts over at least 1,000 hours of operation.
15 . The system of claim 14 , wherein the color shift is predicted based on a measurement of an actual color shift of sample phosphor-containing white LEDs of the kinds of the two or more phosphor-containing white LEDs over at least 2,000 hours but less than 8,000 hours of operation.
16 . The system of claim 13 , wherein the predicted color shift is predicted based on a model.
17 . The system of claim 16 , wherein the model includes a Differential Chromaticity Algorithm (DCA) model, in which chromaticity shifts depend linearly on time.
18 . The system of claim 17 , wherein the two or more phosphor-containing white LEDs are combined based on a predicted lumen maintenance over time for each of the LEDs, and
the lumen maintenance is an exponentially decaying lumen maintenance.
19 . The system of claim 17 , wherein the model is based on either (X, Y, Z) tri-stimulus coordinates, or (Y, u, v)-coordinates, or both.