The term dichroism comes from the Greek and in physics means the two-color nature of crystals when light passes through them. Dichroic filters are filters for color separation based on dielectric interference. They are colored filters that reflect the wavelength of one color and transmit all other wavelengths.
Dichroic filters or dichroic mirrors are used in fiber amplifiers in optical transmission technology, displays and projectors. They operate without absorption, have high light transmission and excellent color accuracy.
Their selectivity is very high, reaching about 80% transmittance at a wavelength change of a few nanometers. Dichroic filters are available as low-pass, high-pass or band-pass filters.
Since dichroic filters always filter out only one color from the light, three dichroic filters are needed in projection technology to produce the three primary colors( RGB), with the middle wavelength range for green being realized by a bandpass filter.