They are typically used for monochrome cameras in order to filter light from the entire spectrum in such a way to produce something like coloured illumination.
The filter glasses (very often coloured glasses by Schott or Hoya) are red, green, orange, blue, or yellow. They let the wavelengths of their own colours pass to the greatest extent (approx. 90 per cent) and block any other. A portion of the rays are reflected at the glass surface. If you use a colour filter with white illumination, you must expect a significant loss of light. They work according to the principle of subtractive colour mixing and due to their design they are not as narrow-banded as interference filters.
This usually refers to high pass filters which let pass high wavelength ranges of the spectrum. They are normally used in combination with infrared lighting. The transmission in infrared radiation is at the maximum, daylight and UV are blocked and not registered by the camera sensor. Daylight influences are almost completely avoided in this way.
Non-visible infrared lighting is used wherever there is much extraneous light (machines close to windows or skylight) or when industrial lighting could disturb the operators (at a manual work station). Depending on the wavelength ranges of the infrared lighting used, there are suitable filters which let pass the light only from 800 or 900 nm.
These filters have a deep red colour and are therefore not suitable for colour cameras.
Vision-Doctor.com is a private, independent, non-commercial website project without customer support.
For the best advice, training and sales of optical filters please click here.
(external link partner website in Europe)