Dichroic filters, also known as interference filter, is an accurate colour filter used to selectively pass light of a small range of colours while reflecting other colours. They are known to be characterised by the colours of light that they reflect, rather than the colour they pass.
Dichroic reflectors known as cold mirrors are commonly used behind a light source to reflect visible light forward while allowing the invisible infrared light to pass out of the rear of the fixture. Such an arrangement allows intense illumination with less heating of the illuminated object. Many quartz-halogen lamps have an integrated dichroic reflector for this purpose, being originally designed for use in slide projectors to avoid melting the slides, but now widely used for interior home and commercial lighting.
Dichroic Mirrors have substantially different reflection properties for two wavelengths. They are usually dielectric mirrors with a suitable thin-film design. For example, they can be used as harmonic separators in setups for nonlinear frequency conversion.