Total Internal Reflection is a phenomenon that takes place when light shines through two mediums and at the boundary all light is reflected. TIR requires two conditions to be met in order to take place, the light must move from the denser medium to the less dense medium and the angle of incidence is greater than the critical angle. The critical angle is the angle between mediums where the angle of incidence causes an angle of refraction of 90 degrees.
How does TIR apply to light guides?
For a light guide to function the TIR physics law must be utilized using the medium of the light guide to that of air. The goal for the light guide is to have the light reflect inside and then exit the light guide at an accepted angle, this will give the light guide good brightness. As the light from the LED moves into the light guide we must take of advantage of TIR to keep the light inside the light guide to obtain the best brightness and uniformity.
Here, at Global Lighting Technologies we use an array of components and techniques to ensure the efficiency of our light guides. Micro-optical extraction features are created on our light guides to redirect light and minimize light loss (See Figures 1 & 2). Back reflectors, edge reflectors, diffusers and other films are used to redirect light back into the light guide for maximum efficiency. (See Figure 4) We also consider the shape of the light guide itself; we can produce flat, tapered, and wedge-shaped light guides which will influence the directionality of the light. (See Figure 3) The positioning of the LED in is also taken into consideration to ensure the most uniform, bright light guide possible.