Reflectance

Reflectivity and reflectance are often used interchangeably, but they refer to distinct concepts in the field of optics. Reflectivity is an intrinsic property of a material, describing its ability to reflect incident light. It is defined as the ratio of the reflected power to the incident power on the surface of a material, considering only the properties of the material itself without regard to the conditions of the light or the environment.

Reflectance, on the other hand, is a measure of how much light is reflected by a surface under specific conditions. It accounts for the angle of incidence, the wavelength of the light, and the surface characteristics. Reflectance is the ratio of the reflected intensity to the incident intensity and can vary depending on the external factors affecting the surface.