What is Luminance?


The apparent brightness of an object that appears to the human eye is known as Luminance. What we see is a pattern of varying luminance when you look at the world (ignoring the colour component). What you are able to see on this page is the luminance of black letters compared to the luminance of the white screen. The intensity or the photoelectric effect that is measured on a surface at a specific position is known as illuminance.

In simple words, luminance is the intensity of the emitted light from a surface per unit area in a particular direction that can be considered for its definition. It provides the amount of light that passes through, is reflected, and falls within a given solid angle. The SI unit of Luminance is candela per square meter (cd/m2). The measure of the total light output of a luminous source is known as Luminous Flux.

The luminance of the surface depends on the following factors.

  1. Nature of the surface.
  2. The Luminous flux that is incident on the unit area of the surface.

Light Meter:

A light meter is a device used to measure the amount of light. It is categorized into two types known as, reflected light meter and incident light meter.

  • The Reflected light meters calculate the light that is reflected and needs to be photographed.
  • The incident light meters calculates the amount of light that falls on the subject by using the integrated sphere.

Luminance Formula

Following is the table explaining the formula of luminance with notations:

\(L=K_{m}\int L_{e\lambda }V(\lambda )\Delta \lambda\)


  • L is the luminance
  • Km is the maximum luminance efficiency
  • L is the spectral radiance
  • V(λ) is the luminance efficiency function
  • λ is the wavelength
  • Δλ is the wavelength interval over which the integration is taking place

Uses of Light Meter:

  • Light meters are also used in measuring illumination in the interior and switch off the output of the fitting light. This increases the efficiency of the system by reducing or lowering the burden of energy building.
  • Photography is one of the major uses of a light meter. It is used to find an appropriate exposure of light in photography. A light meter consists of an analog or digital computer distinctively that helps the photographer to determine the speed of shutter and f-number that needs to be selected for best exposure under a particular lighting situation.
  • Cinematography and science design are the other situations where the light meter has its application. These are also used in the areas of lighting to ensure minimum wastage of light, plant growing to ensure appropriate light levels and light pollution outdoors.

Stay tuned with BYJU’S to learn more about luminance, a reflection of light, and much more.

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