Patent ID: 11914180

Abstract:
An optical filter has a back-scattering property. The linear transmittance thereof to light of at least some avelengths in the wavelength range of 760-2000 nm is 60% or higher. The azimuth is 20° from an incidence plane when the polar angle of the direction of incidence of incident light is 0°. The value of a bidirectional reflectance distribution function in the direction ‘here the polar angle is −60’ is BRDF (0°; 20°, −60°). The azimuth is 20° from an incidence plane when the polar angle of the direction of incidence of incident light is 30°. The value of a bidirectional reflectance distribution function in the direction where the polar angle is −60° is BRDF (30°; 20°, −60°). The azimuth is 20° from an incidence plane when the polar angle of the direction of incidence of incident light is 60°.