The neutral density filter uses the absorption or reflection characteristics of light to attenuate the light intensity. After the light in the visible region to the near-infrared region passes through the neutral density filter, different wavelengths are attenuated in the same proportion. Make the optical element maintain approximately equal light energy transmittance in a wide wavelength band.

ND filter's role is to attenuate the energy of the incident beam. This attenuation effect is non-selective, that is, in the effective range of action on a variety of different wavelengths of light are equally attenuated and uniform, so from the surface looks black or gray, it only reduces the light intensity and no effect on the color of the target object.