Interference filters rely on harmonic interference between waves to provide very narrow passbands. Thin metal films are spaced half the desired wavelength apart by a dielectric spacer. Interference filters are capable of bandwidths less than 10 nm. Absorptive filters typically consist of glass that has been doped with a concentration of dye that absorbs particular colors. Since spectral transmission varies logarithmically with thickness, the band pass can be reduced by thickening the filter.
Internal transmittance is greater than external transmittance due to reflection losses.
Multiple color filters can be layered to match a desired function, such as the CIE photopic response, which defines the eye's sensitivity to color. The combined spectral response is the product of the filter's transmission and the spectral responsivity of the detector. International Light Filters International Light optical filters are the building blocks that allow a myriad of applications with one or more standard IL1700 detector. Unmounted filters and empty filter rings are also available. Listed below is a representative selection of the many filters that are available from stock for custom spectral responses not found as standard configurations.