The luminance meter is a commonly used test instrument in the fields of lighting engineering, light sources, and light-emitting devices, film and television, traffic signals, architecture, atmospheric photometry, etc.

The Luminance meter mainly uses a pair of light holes with a certain distance to receive the luminous flux of a fixed solid angle and a fixed light projection area. This value does not change with the distance of the object, as long as the surface area of the object is large enough. In order to aim at the object to be measured, an imaging system is often used.
The measured light source of the Luminance meter is imaged on the mirror with a hole (front light hole) after passing through the objective lens, and part of it is received by the human eye through the mirror and eyepiece, so as to aim and monitor the clear imaging surface and the mirror with a hole coincident; Part of the light passes through the small hole on the mirror and reaches the V(λ) receiver through the rear light hole.
The Luminance meter is displayed with an analog or digital meter. It has a wide range of uses in TV, medical X-ray, CRT and electroluminescence, fluorescent substances, and other measurements.
Through the above introduction and analysis of What the Luminance meter do, hope it helps you.