Methods, apparatus and articles of manufacture to calibrate lighting units
View Patent ↗A system and appertaining method calibrate a color LED light unit comprising at least first-, second-, and third-color LEDs, comprising: a) defining a target color on a color map to calibrate; b) selecting initial calibration coefficients associated with the target color; c) storing the initial or updated calibration coefficients in a non-volatile memory of the light unit; d) controlling the light unit to drive the LEDs to attempt to emit the target color, producing an attempted color, utilizing the calibration coefficients; e) measuring the attempted color to determine if it matches the target color within a predefined tolerance; f) if the attempted color matches the target color, then terminating the method; g) if the attempted color does not match the target color, then performing the following; h) selecting a color component; i) adapting at least one calibration coefficient associated with the selected color component; and j) performing (c)-(i) again.
1. A method for calibrating a color LED light unit comprising at least first-, second-, and third-color LEDs, comprising:
a) defining a target color on a color map to calibrate that requires a contribution from at least the first- and second-color LEDs, wherein the defined target color is one of at least three target colors and the three colors define a color gamut as three points of vertices of a triangle;
b) selecting first and second initial calibration coefficients associated with the first- and second-color contributing LEDs that contribute to the target color;
c) storing the initial or updated first and second calibration coefficients in a non-volatile memory of the light unit;
d) controlling the light unit to simultaneously drive the first and second LEDs to attempt to emit the target color, producing an attempted color, utilizing the calibration coefficients;
e) measuring the attempted color to determine if it matches the target color within a predefined tolerance;
f) if the attempted color matches the target color, then terminating the method;
g) if the attempted color does not match the target color, then performing the following;
h) selecting a color component corresponding to the first-color LED;
i) updating the first calibration coefficient associated with the selected color component;
j) performing (c)-(f) immediately again;
k) if the attempted color does not match the target color, then performing the following;
l) selecting a color component corresponding to the second-color LED;
m) updating the second calibration coefficient associated with the selected color component;
n) performing (c)-(f) again;
performing (a)-(j) for one or more target colors of the at least three target colors;
measuring a statistically significant plurality of LEDs of each color class;
determining a variance for each color class LED;
defining a worst case color gamut within a predetermined probability; and
defining the three points to specifically bound the worst case color gamut.
2. The method according to claim 1 , wherein the first color is red, the second color is blue, and the third color is green.
3. The method according to claim 2 , wherein the LED light unit further comprises a white LED.
4. The method according to claim 3 , further comprising determining, by a controller, which of the LEDs to turn on and at what intensities based on the following mathematical equations:
F ( W )= W−k ww W (1)
F ( R )=( R−k rr R )+ k rg G+k rb B k rw W (2)
F ( B )=( B−k bb B )+ K br R+k bg G k bw W (3)
F ( G )=( G−k gg G )+ k gr R+k gb B+k gw W (4)
where the coefficients:
k ww
k rw
k rr
k rb
k rg
k bw
k br
k bb
k bg
k gw
k gr
k gb
k gg
are calibration coefficients determined by a calibrator and represent the inter-dependence of the various colored LEDs in generating a particular desired color;
W, R, B and G collectively represent the desired color to be emitted; and
F(W), F(R), F(B) and F(G) represent the light intensity to be emitted by a white LED, a red LED, a blue LED and a green LED, respectively.
5. The method according to claim 1 , wherein the controlling of the light unit is performed using variations in a pulse width in a pulse-width-modulated (PWM) signal.
6. The method according to claim 5 , wherein the variations comprise at least 1024 different values.
7. The method according to claim 1 , wherein the initial or updated first and second calibration coefficients are represented by 7-, 8-, 16-, or 24-bit values.
8. The method according to claim 1 , wherein the determining a color match comprises:
matching to a level that is indistinguishable to the human eye.
9. The method according to claim 1 , wherein the determining a color match comprises:
matching to a predefined multiplier of a MacAdam Ellipse.
10. The method according to claim 1 , wherein the vertices represent virtual primary colors.
11. The method according to claim 10 , wherein the vertices require driving of the red, green, and blue LEDs with non-zero values.
12. A non-transitory computer program product, comprising a computer usable medium having a computer readable program code embodied therein, said computer readable program code adapted to be executed to implement the method according to claim 1 .