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Side Collimated backlight with RGB LED lightsource Disclosure Number: IPCOM000016469D
Publication Date: 2003-Jun-24
Document File: 3 page(s) / 51K

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The side collimated LED backlight was developed for LCD displays. The backlight is a kind of direct backlight that enables higher optical efficiency compare to the backlight that use light guide.

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Side Collimated Backlight with RGB LED Light Source

Takaaki Yagi

Lumileds Lighting Japan

1. Back light Structure

Side Collimated Backlight is designed for three primary color light sources. The light source colors are red, green and blue LED’s. The LED light is easy to collimate in a small area because the light has some direction when it is compared to CCFL light source that emits light all direction. This design utilizes this optical property.


Fig.1 shows the structure of a side-collimated backlight. The LED light source is placed at both sides of the backlight. The reflector mirrors surround the LED’s. The reflector mirrors forms collimator mirror. The collimator mirror aperture usually becomes larger as the distance between light source and mirror position increases.


Fig.2 shows the cross sectional view of collimator mirror and it’s light trace. This is the typical idea for collimator design. The side-collimated backlight utilizes this idea.

2. Mirror design

In the backlight design, the side mirror has two purposes. The first one is collimator. The second one is direct light shielding to the top diffuser. The direct light creates poor color uniformity at the screen. The collimator is made up top and bottom mirror. The cross-sectional structure is shown in Fig.3.


The top mirror plays mainly direct light shielding and the bottom mirror plays collimator. The light has to travel more than the RGB light source unit length for making uniform intensity of three primary colors. The RGB light source unit length in this design is 50mm.


Fig.4 shows one example RGB LED light source array. Lumileds Lighting has developed the light source for backlight using high power RGB LED array as shown in Fig.4. The high power LUXEON LED’s are placed as a array on metal core PC board. Light source is made with appropriate number of each color. The light source is 100mm width and RGB unit length is the half of the array width in this case. The minimum direct light path from the light source to the top diffuser designs the top mirror shape. The minimum light path has to be larger than the LED light source unit length that is 50mm. The minimum light path becomes longer when the mirror is steep and long. The specular mirror surface is preferable so as not to scatter light to neighborhood area. The light scatte...