Fluid light controlling medium for a vehicle rearview mirror

Claim 1

A fluid composition for use as a light attenuating medium in a rearview mirror consisting essentially of: (a) a carrier fluid, the major component of which is propylene carbonate, such that said carrier fluid has a freezing point ≦-30° C., a boiling point ≧80° C., and a viscosity within 5° C. of the freezing point thereof of up to 50 centipoise; (b) a light absorbing dye in solution, rather than in dispersion, in said carrier fluid consisting of an azo, anthraquinoid, phthalocyanine or 1,2-chrome dye or a mixture of two or more thereof, said dye or mixture of dyes remaining in solution at a temperature below -30° C. and having an absorbance characteristic when combined with the other fluid components according to Beer-Lambert's Law: Ix=Ioe.sup.-acx wherein Ix=intensity of illumination after-traveling through the fluid; Io=initial intensity of illumination; α=average absorbance coefficient of the dye or dye mixture in the visible range of radiation; c=concentration of the dye or dye mixture; and x=light pathlength through the light absorbing medium such that αcx=A where A has a value in the range 0.05 to 11.0 and where the maximum value of A for the day position of the mirror is 0.28 and where the minimum value of A for the night position of the mirror is 2.00; and (c) a U.V. stabilizing agent in solution in said carrier fluid which is a benzophenone, benzotriazole or organo-nickel complex.