Near Infrared transmitting filters reflect virtually all visible light while allowing only near infrared photons to pass through them.
NIR FILTERS FOR NEAR INFRARED ILLUMINATION
A popular and sometimes inexpensive method for performing night vision is by near infrared illuminations. In this mehtod, a standard high power lamp that is covered by the near infrared filter designed to pass the lamp's near infrared radiation and block the visible light component is used. Providing supplemental infrared illumination of an appropriate wavelength not only eliminates the variability of available ambient light, but also allows the observer to illuminate only specific areas of interest while eliminating shadows and enhancing image ontrast.
The supplemnetal near infrared lighting not only improves the quality of image intensifier devices but also permits the use of solid state cameras, which also have the ability to convert near infrared images to visible.
NIR FILTERS FOR OPTHALMIC DEVICES
Opthalmic deviceslike "iris scanners" use near Infrared (NIR) imaging by emitting 750nm wavelength low-power light. This is done because dark-brown eyes, possessed by the majority of the human population, reveal rich structure in the NIR but much less in the visible band (400 700nm), and also because NIR light is invisible and unintrusive. A further important reason is that by allowing only this selected narrow band of illuminating light back into the camera via NIR filters, most of the ambient corneal reflections from a bright environment are blocked from contaminating the iris patterns