What is Light Scattering?

While light scattering can be a tool for many illumination applications, it can also be a problem for imaging applications. Surfaces may scatter light in a way that creates additional paths for the light to travel back into the optical system, creating visual artifacts known as ghost images on the final image. Mechanical housing also can cause unwanted scattering within the system, and those are usually accounted for in illumination ray tracing applications, which track scattering events.

When using structures such as baffles to minimize ghost images, ray tracing the system to perform stray light analysis can help to rid the image of visual artifacts in the design. To do this, you can use illumination design software that provides a ray path analysis, which tracks every possible path the light can take in an imaging system, accounting for every structure in the design, including the mechanical housing of a system. The software can look at the power level of the ghost images generated, pinpoint where they come from, and enable designers to eliminate the offending surfaces or create structures that do the same, either manually or using optimization techniques.

Light scattering can be measured using a scatterometer, which takes 2D or 3D measurements from one or more sources emitting onto a surface or into a medium and records the angular distribution of light (intensity) that is reflected back and/or transmitted through. The results can be recorded in many ways, but one common method is to record reflected light is as Bidirectional Reflected distribution Function (BRDF) and transmitted light as Bidirectional Transmitted Distribution Function (BTDF). Together, these two functions become the Bidirectional Scattering Distribution Function (BSDF). Depending on the measurement method, this function can define the light scattering of a surface, a medium, or both combined. Depending on the nature of the sample measured, it is possible to separate which of the two is the main contributor to the scattering effect. After the measurements are done, it is possible to establish a mathematical fit to the scattering profile of the material or surface, which can be used in simulations.