Light traps are an essential part of any reflectance spectrometry system. They can be used to establish the sphere zero. In reflectance, all incident light should hit the sample. In most sphere systems, however, some light hits the sphere wall instead of the sample due to scatter from optical components. The system operator must use a light trap to quantify residual light, which can be subtracted from both sample and reference scans.
Light traps are also useful in removing the transmitted component in translucent samples, so that radiation cannot reflect inside the sample compartment and return to the sphere.
Avian Technologies offers two types of light traps: a black glass trap, and a diffuse coating trap.
Black Glass Traps
The black glass trap, modeled after the Clarke-Compton light trap designed by the National Physical Laboratory, uses a cavity with two pieces of black glass to form a semi-cone. The light enters the cavity and is absorbed by multiple reflections off the black glass. Typically, such light traps give a reflectance in the order of <0.1%. The Avian Technologies design is compact (25 mm high, 44 mm square) and can be designed to fit any sample holder configuration.
The diffuse coating trap offered is a simple box that has been coated with a very low reflectance diffuse coating or material. While not as efficient as the black glass trap, Avian Technologies “diffuse trap” is still highly efficient due to the use of a proprietary material that is <1.3% reflective and highly diffuse. The overall efficiency of this trap is >99.5% (ie. <0.5%R).