This optical filter has a back-scattering property, and the linear transmittance thereof to light of at least some wavelengths in the wavelength range of 760-2000 nm is 60% or higher. Where: the azimuth from an incidence plane when the polar angle of the direction of incidence of incident light is 0° is 20°, and the value of a bidirectional reflectance distribution function in the direction where the polar angle is −60° is BRDF (0°; 20°, −60°); the azimuth from an incidence plane when the polar angle of the direction of incidence of incident light is 30° is 20°, and the value of a bidirectional reflectance distribution function in the direction where the polar angle is −60° is BRDF (30°; 20°, −60°); and the azimuth from an incidence plane when the polar angle of the direction of incidence of incident light is 60° is 20°, and the value of a bidirectional reflectance distribution function in the direction where the polar angle is −60° is BRDF (60°; 20°, −60°), then, for the incident light having at least some wavelengths in the wavelength range of visible light, |BRDF (0°; 20°, −60°)−BRDF (30°; 20°, −60°)|/BRDF (0°; 20°, −60°) is 1.0 or lower, and |BRDF (0°; 20°, −60°)−BRDF (60°; 20°, −-60°)|/BRDF (0°; 20°, −60°) is 1.0 or lower.