Methods, apparatus and articles of manufacture to calibrate lighting units

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;

b) selecting initial calibration coefficients associated with the target color;

c) storing: 1) the initial, or 2) updated calibration coefficients in a non-volatile memory of the light unit;

d) controlling the light unit with a controller to drive the LEDs to attempt to emit the target color, producing an attempted color, utilizing one of the initial and updated 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.1) selecting a first color component;

i.1 adapting at least one calibration coefficient associated with the selected first color component by a first color component first amount;

j.1 a performing (c)-(g) again;

h.2) selecting a second color component that is different from the first color component;

i.2) adapting at least one calibration coefficient associated with the selected second color component by a second color component first amount;

j.2) performing (c)-(g) again;

h.3) selecting the first color component;

i.3) adapting the at least one calibration coefficient associated with the selected first color component by a first color component second amount that is smaller than the first color component first amount and avoids an overshoot of the target color;

i.3) performing (c)-(g) again;

h.4) selecting the second color component;

i.4) adapting the at least one calibration coefficient associated with the selected second color component by a second color component second amount that is smaller than the second color component first amount and avoids an overshoot of the target color;

j.4) performing (c)-(g) again;

wherein a path in a color space of the attempted colors forms: a) a converging winding path when only two color components are utilized; and b) a converging spiral when three color components are utilized.

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 , wherein the controller determines 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 and updated calibration coefficients are represented by 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 , further comprising:

performing (a)-(j) for one or more additional target colors.

11. The method according to claim 10 , wherein at least three colors are used as target colors, and the three colors define a color gamut as three points of vertices of a triangle.

12. The method according to claim 11 , wherein the vertices represent virtual primary colors.

13. The method according to claim 12 , wherein the vertices require driving of the red, green, and blue LEDs with non-zero values.

14. 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 .

15. 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;

b) selecting initial calibration coefficients associated with the target color;

c) storing: 1) the initial, or 2) updated calibration coefficients in a non-volatile memory of the light unit;

d) controlling the light unit with a controller to drive the LEDs to attempt to emit the target color, producing an attempted color, utilizing one of the initial and updated 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;

j) performing (c)-(i) again;

performing (a)-(j) for one or more additional target colors, wherein at least three colors are used as target colors, and the three colors define a color gamut as three points of vertices of a triangle;

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 tree points to specifically bound the worst case color gamut.

16. A system for calibrating a color LED light unit, wherein:

the color LED light unit comprises:

at least first-, second-, and third-color LEDs; and

a non-volatile memory; and

the system comprises:

a) a target defining unit that defines a target color on a color map to calibrate;

b) an assigning unit that selects initial calibration coefficients associated with the target color and stores: 1) the initial, or 2) updated calibration coefficients in the non-volatile memory;

c) a controller that controls the light unit to drive the LEDs to attempt to emit the target color, producing an attempted color, utilizing one of the initial and updated calibration coefficients;

d) a sensor that measures the attempted color to determine if it matches the target color within a predefined tolerance; and

e) a selection and adaption unit configured such that:

f) if the attempted color matches the target color, then the system ceases performing calibration;

g1) if the attempted color does not match the target color, then:

h1) a selection unit selects a first color component; and

i1) an adaption unit adapts at least one calibration coefficient associated with the selected first color component by a first color component first amount;

(f) is performed again;

g2) if the attempted color does not match the target color, then:

h2) the selection unit selects a second color component that is different from the first color component; and

i2) the adaption unit adapts at least one calibration coefficient associated with the selected second color component by a second color component first amount;

(f) is performed again;

g3) if the attempted color does not match the target color, then:

h3) the selection unit selects the first color component; and

i3) the adaption unit adapts the at least one calibration coefficient associated with the selected first color component by a first color component second amount that is smaller than the first color component first amount;

(f) is performed again;

g4) if the attempted color does not match the target color, then:

h4) the selection unit selects the second color component; and

i4) the adaption unit adapts the at least one calibration coefficient associated with the selected second color component by a second color component second amount that is smaller than the second color component first amount;

wherein a path in a color space of the attempted colors forms: a) a converging winding path when only two color components are utilized; and b) a converging spiral when only three color components are utilized.