Single fibers with larger single diameters are used as core fibers. Bundling individual fibers is a common practice. For sidelight applications, the fiber doubles as the output fixture. Most output fixtures used today are based on tradition lighting systems design. In addition, a coupler allows several large core fibers to be attached to a single illuminator.
All fiber optics work on the principal of total internal reflection.
When a light traveling in one material approaches another, it is bent somewhat. If the light approaches the second material at a shallow enough angle, then it does not enter the second material but is reflected back into the first. A typical fiber optic lighting system is about 15 percent efficient overall, but that level will increase in the near future. To supply a particular quantity of light for a task, one measures illuminance, which is defined as flux density on a surface or lumens. The designer should assume a metal halide light will provide 80 lumens per watt.