What Are Light Guides
Light Guides are a clever method of directing light in applications where direct light from the light source can not be used due to physical, economic, aesthetic or other restrictions.Light guides (also called light pipes) are a major component in edge-lit LCD display back lights where there is a CCFL or LED light source at one or two opposite edges of a light guide, which extracts the light towards the viewer. This approach allows for the use of less powerful light sources while maintaining high screen uniformity and very thin display profiles.
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| Basic single-edge-lit light guide that extracts light from one side |
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| Rectangular display guide with visible extraction side |
With the growing popularity of Solid State Lighting (LEDs and OLEDs), light guides are becoming increasingly sought for the creation of ultra-thin sleek and stylish lighting and signage fixtures.
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| Light guide that extracts light from both sides |
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| Fusion Optix Direct/Indirect fixture utilizing 2-side light-extracting guide. LED light sources are hidden in the cylindrical bezels along the edges of the fixture. |
How Light Guides Work
Light guides rely on the combination of total internal reflection (TIR) and a light extraction method to create a flat thin evenly emitting surface. For TIR to occur light has to strike the inner surface of the guide at an angle smaller than a specific critical angle. All light rays that strike the surface at angles higher than the critical angle are transmitted.
What sets apart light guides from mere plastic rectangles is that light guides greatly increase the chance of light being transmitted through the extraction sides. This can be achieved in two ways:
Critical Angle Transmission
In CAT numerous imperfections are introduced at the extraction surface that increase the chance of light reaching critical angle. Depending on the light source, light guide dimensions and other factors, special imperfection patterns and shapes are developed to ensure maximum light extraction.
Frustrated Internal Reflection
In FIR a scattering material is applied to the extraction surface. The scattering material has different optical density from both the light guide and air, which results in light being transmitted from the guide to the scattering material.
