An optical filter having back-scattering characteristics, wherein the optical filter comprises a matrix and fine particles dispersed in the matrix; wherein the optical filter has a regular transmittance of 60% or higher for light having a wavelength in at least a part of a wavelength range not shorter than 760 nm and not longer than 2000 nm, and wherein with settings that: in the case where incident light has a polar angle of 0° in a direction of incidence, a bidirectional reflectance distribution function value,BRDF, in a direction having an azimuth of 20° from a plane of incidence and having a polar angle of -60° is BRDF (0°; 20°, -60°), in the case where the incident light has a polar angle of 30° in the direction of incidence, the bidirectional reflectance distribution function value in the direction having an azimuth of 20° from the plane of incidence and having a polar angle of -60° is BRDF (30°; 20°, - 60°), and in the case where the incident light has a polar angle of 60° in the direction of incidence, the bidirectional reflectance distribution function value in the direction having an azimuth of 20° from the plane of incidence and having a polar angle of -60° is BRDF (60°; 20°, - 60°), in the case where the incident light has a wavelength in at least a part of a visible light wavelength range, |BRDF (0°; 20°, -60°) - BRDF (30°; 20°, -60°)|/BRDF (0°; 20°, -60°) is 1.0 or smaller, and |BRDF (0°; 20°, -60°) - BRDF (60°; 20°, -60°)|/BRDF (0°; 20°, -60°) is 1.0 or smaller; wherein the fine particles form at least a colloidal amorphous array so as to not cause Bragg reflection and a transmittance curve of the filter in a visible light wavelength region includes a curved portion where the regular transmittance is decreased monotonically from a longer wavelength side to a shorter wavelength side, and the curved portion is shifted to the longer wavelength side as an angle of incidence is increased; and wherein the fine particles have an average value of inter-gravitational centre distances of 150 nm or longer on a cross-section vertical to a planar direction of the filter. wherein the optical filter comprises a matrix and fine particles dispersed in the matrix; wherein the optical filter has a regular transmittance of 60% or higher for light having a wavelength in at least a part of a wavelength range not shorter than 760 nm and not longer than 2000 nm, and wherein with settings that: in the case where incident light has a polar angle of 0° in a direction of incidence, a bidirectional reflectance distribution function value,BRDF, in a direction having an azimuth of 20° from a plane of incidence and having a polar angle of -60° is BRDF (0°; 20°, -60°), in the case where the incident light has a polar angle of 30° in the direction of incidence, the bidirectional reflectance distribution function value in the direction having an azimuth of 20° from the plane of incidence and having a polar angle of -60° is BRDF (30°; 20°, - 60°), and in the case where the incident light has a polar angle of 60° in the direction of incidence, the bidirectional reflectance distribution function value in the direction having an azimuth of 20° from the plane of incidence and having a polar angle of -60° is BRDF (60°; 20°, - 60°), in the case where the incident light has a wavelength in at least a part of a visible light wavelength range, |BRDF (0°; 20°, -60°) - BRDF (30°; 20°, -60°)|/BRDF (0°; 20°, -60°) is 1.0 or smaller, and |BRDF (0°; 20°, -60°) - BRDF (60°; 20°, -60°)|/BRDF (0°; 20°, -60°) is 1.0 or smaller; in the case where incident light has a polar angle of 0° in a direction of incidence, a bidirectional reflectance distribution function value,BRDF, in a direction having an azimuth of 20° from a plane of incidence and having a polar angle of -60° is BRDF (0°; 20°, -60°), in the case where the incident light has a polar angle of 30° in the direction of incidence, the bidirectional reflectance distribution function value in the direction having an azimuth of 20° from the plane of incidence and having a polar angle of -60° is BRDF (30°; 20°, - 60°), and in the case where the incident light has a polar angle of 60° in the direction of incidence, the bidirectional reflectance distribution function value in the direction having an azimuth of 20° from the plane of incidence and having a polar angle of -60° is BRDF (60°; 20°, - 60°), in the case where the incident light has a wavelength in at least a part of a visible light wavelength range, |BRDF (0°; 20°, -60°) - BRDF (30°; 20°, -60°)|/BRDF (0°; 20°, -60°) is 1.0 or smaller, and |BRDF (0°; 20°, -60°) - BRDF (60°; 20°, -60°)|/BRDF (0°; 20°, -60°) is 1.0 or smaller; wherein the fine particles form at least a colloidal amorphous array so as to not cause Bragg reflection and a transmittance curve of the filter in a visible light wavelength region includes a curved portion where the regular transmittance is decreased monotonically from a longer wavelength side to a shorter wavelength side, and the curved portion is shifted to the longer wavelength side as an angle of incidence is increased; and wherein the fine particles have an average value of inter-gravitational centre distances of 150 nm or longer on a cross-section vertical to a planar direction of the filter.