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Interference filters are commonly used as wavelength selectors in a variety of quantitative chemical assays. They are used extensively in clinical chemistry, water analysis, quality control, and in general purpose laboratory colorimeters. In addition, interference filters are used to select discrete spectral lines from arc or gas discharge lamps (Hg, Xe, Cd, etc.) and to isolate a particular line from Ar, Kr, Nd-Yag, and other lasers. They are often used in conjunction with laser diodes and LEDs.

Interference or bandpass filters are produced by a series of carefully controlled vacuum depositions of various dielectric (non-conductive) materials on a glass plate. Each deposition is only a few nanometers thick and is made from a material with a known refractive index. After the required number of layers have been deposited, a second glass plate is laminated to the first, to seal out humidity and protect the deposited thin films. As light passes through the filter, it is affected by each film interference due to differences in refractive indices. These differences cause destructive interference at some wavelengths, resulting in high reflectance, while causing constructive interferences at other wavelengths, resulting in high transmittance.

All filters have a clear area (scribe) of approximately 1.5mm around their circumference or perimeter. Filters will function with either side facing the source. We recommend, however, orienting the "mirror-like" side toward the source to minimize any thermal effects. If the source overfills the actual filter area, beam vignetting may be necessary.