LED illumination - wavelengths and filtering
As coloured LED light (i.e. red, green, blue) is emitted in small wavelength bands, colour or interference filters can be used to suppress any ambient light not in the chosen LED wavelength. The result is the ability to reduce the total intensity of the LED illuminator without ambient light causing a problem. Special features of the object are still preserved with good contrast and the colour of an LED light can also be used to increase the contrast in monochrome images.