An apparatus for and method of calculating an integrated index of a transparent, translucent or opaque material for a desired wavelength range, the method comprising measuring a filtered value of the material as a function of wavelength within the desired wavelength range and calculating a protection...http://www.google.co.uk/patents/US20030095256?utm_source=gb-gplus-sharePatent US20030095256 - Method and apparatus for quantifying an "integrated index" of a material medium
