Koninklijke Philips Corporation N.v.

Philips Lumileds Lighting Company LLC

Robert Hendriks

Martijn H R Lankhorst

Pieter Grootes

An LED light source for LCD backlighting is described that recalibrates itself over time so that color and brightness uniformity across the backlight is maintained over the life of the backlight. The backlight contains clusters of red, green, and blue LEDs, each cluster generating a white point. In one embodiment, each color in a cluster has its own controllable driver so that the brightness of each color is a cluster is separately controllable. One or more optical sensors are arranged in the backlight, and the sensor signals are detected by processing circuitry to sense the light output of any LEDs that are energized in a single cluster. The measured white point and flux are compared to a stored target white point value and flux for that cluster. The currents to the RGB LEDs are then automatically adjusted to achieve the target level for each cluster. This process is applied to each cluster in sequence until the recalibration is complete. The recalibration takes place at various times over the lifetime of the backlight to offset the effects of LED degradation over time. Variations of this technique are also described.

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Overlangel, Netherlands

Robert Hendriks