By way of a simple example of the optical perfromance of the BEF, a simple system was built using the BEF_Model.zmx file.

A source object was been placed inside the BEF, at the top of one side. The source used Sobol sampling, and simple splitting was turned on. Neither of these are essential, but they are very useful, and very powerful features to enhance the study of illumination systems.

No attempt was made to make this a realistic model of an LCD illumination screen: rather this is just a simple demonstration of the optical properties of brightness enhancement films. It also shows just how efficient the Array object is in both memory usage and ray-tracing speed: a 5mm x 5mm piece of BEF requires 417² = 173,899 prisms. A 0.5 meter x 0.5 meter square piece (by no means unrealistic) requires 1.7 GIGA-prisms! This would be extremely unweildy to model any other way. As will be seen in this example, ZEMAX handles this with little extra memory requirement and very fast ray-tracing speeds, thanks to the internal architecture of the array object.

All the sides of the backing material object, except the one in contact with the array object, were set to be reflective:


as a result, rays can only escape via the prism face of the BEF. Note that no thin-film coatings were applied, because none are used in the manufacture of the BEF. They can be easily added to the ZEMAX model if needed.

Here is an example of the ray-tracing in the BEF:



note that the 'do not draw' property has been set on the array object so that the bounding box is not drawn either: however the multiple TIR-ing of the rays at the prism array can be clearly seen, even though the prism array is not drawn. The outcoupling of light at near to normal incidence to the BEF object can also be seen. In comparison, if the array object is set to 'rays ignore this object' so that there is no prismatic structure, the ray-trace is as follows:



and light is trapped by total internal reflection.

A detector object was also been defined. In the following screenshots, the detector shows the results of tracing 1 million rays. In the absense of the prismatic strucure, little light escapes the plastic sheet, as shown above, but when the prism structure is turned on, we get:



Here is the illuminance (spatial distribution of power) seen on the detector. The source was set to a nominal 1 Lumen output power:



and so a total of 0.3 lm is coupled onto the detector, with a peak illuminance of 484 Lux. The luminous intensity (angular distribution of power) is



The peak luminous intensity of 0.29 Cd occurs on-axis, and that the distribution is more compressed perpendicular to the prisms than parallel.

Again, note that this is just a simple file demonstrating the optical performance of the BEF array, and is not a model of a full LCD device.