COLOR FEEDBACK OPTICAL SYSTEM FOR DIRECT BACKLIGHT
Publication Date: 2003-Oct-27
The IP.com Prior Art Database
Direct backlight employs light sources placed in an air-filled cavity behind the LCD. The ray pattern of the light sources in combination with the shape, reflective material of the cavity and the optical properties of the front diffuser sheet create a desired luminance profile behind the LCD.
LEDs can be used as a light source in this system. Contrary to the edge-lit backlight, there is no need for a separate color mixing arrangement, optical system is very simple and the efficiency is high.
However, just as the edge-lit LED backlight, direct backlight suffers from color variations due to temperature drifts and aging of the individual LEDs. The solution to such drifts is and optical feedback system with a color sensor. In an edge-lit backlight the sensor is placed at the end of the light guide where it receives well-mixed light from all the LEDs. In a direct backlight it is difficult to place the sensor without having some LEDs contributing more to its signal then the others. This leads to incorrect color control.
We propose to use a structure from transparent material effectively sampling the light distribution in the whole backlight or in a large area where the group of LEDs that we wish to control is situated (Figure 1). This structure can guide light to a side of the backlight towards the sensor.
Figure 1. Schematic representation of a direct backlight with optical color feedback using a light sampler.
For coupling the light into the light se...