Photochromic filter assemblies

摘要

An optical device (10) (e.g. the eye) is protected from exposure to very high levels of illumination (12) by the provision of a photochromic filter (11) which attenuates the transmitted visible light. The filter is of limited thickness for maximum efficiency being equal to the penetration depth for the UV activation wavelengths and is situated between lenses which expand and then diminish the incident beam 12 such that the filter is of sufficient area to be below saturation.