Patent ID: 7671542

Claim:
A method for operating a light emitting diode (LED) backlight having a plurality of LED strips, (S i ), wherein i=1, 2, 3, . . . , N, N being a positive integer, wherein each LED strip S i is configured to receive a driving current, C i , and in response thereto, to emit light, L i , wherein the light L i is characterizeable with a chromaticity and a brightness in terms of chromaticity coordinates, Luv i , which is associated with the driving current C i , comprising the steps of: a. supplying each of the plurality of LED strips (S i ) with a corresponding driving current C i by pulse width modulation (PWM) to cause it to emit light L i ; b. imposing a time delay or a phase shift on a PWM driving current C k supplied to an LED strip S k to be monitored, wherein the time delay or the phase shift is chosen so that it has no effect on the chromaticity coordinates Luv k of the light L k emitted from the LED strip S k , wherein k=1, 2, 3, . . . or N; c. measuring the chromaticity coordinates Luv k of the light L k emitted from the LED strip S k when the time delay or the phase shift is monitored; d. comparing the measured chromaticity coordinates Luv k of the light L k with a reference chromaticity coordinates, Ruv k , of light for the LED strip S k ; e. adjusting the PWM driving current C k supplied to the LED strip S k so that the measured chromaticity coordinates Luv k are substantially identical to the reference chromaticity coordinates Ruv k for the LED strips S k ; and f. repeating steps (b)-(e) for each of the rest of the plurality of LED strips (S i ), so as to make light emitted from the plurality of LED strips (S i ) have a substantially uniform chromaticity and a substantially uniform brightness.