Luminance the property of an object that is the apparent brightness as appearing to the human eye. It is a quantitative property that gives the strength of the source light and the quantity that is received by humans. Further, we can measure it with a light meter. There is a formula for it to measure this quantity.


Introduction to Luminance

The luminance is basically the intensity of light which emits from a unit surface area in a particular direction.

The SI unit of luminous Intensity or Luminance is candela per meter square or cd/m². Further, we also refer to it as a nit. It gives the intensity of light that passes through from a source, reflects and falls back within a solid angle. Moreover, the luminance factor depends upon the nature of the surface and also the unit area of the surface on which it emits.

In addition, the total amount of light that is taken as an output from a luminous source is known as the luminous flux.

The SI unit of Illuminance in lux that measures the luminous flux per unit area. It is represented as lumen per square meter of space.  Further, Lux and Lumen are difference analogy. We calculate Lux o the basis of the amount of area which the luminous flux covers. Hence, we can state that a flux of a thousand lumen spread over 1 sq meter radius results in a illuminance of a thousand lux.

Luminance Formula

The luminance formula determines the luminance of a particular source of light. The formula is as follows:



L = Luminance

Km = maximum luminance efficiency

Le lambda = spectral radiance

V (lambda) = luminance efficiency function

Lambda = wavelength

Delta lambda = interval of wavelength within which integration happens

What is a Light Meter?

We use a light meter to measure the amount of light that emits. Further, there is an incident light meter and a reflected light meter. Moreover, these are the two types of light meters used to measure light.

Thus, the incident light meter comes in use to calculate the amount of light which is falling on the subject based on an integrating sphere.

Further, the reflected light meter measures the reflected light and the amount of light that requires to be photographed.

Advantages of Using a Light Meter 

A light meter has many uses in everyday life. Further, as this associate with luminance which is visible light, it comes in use in several fields where light is a major factor.

  • We can use it to measure illuminance. Illuminance is the intensity of light that falls on a surface at a specific position. Moreover, this comes in use in measuring the interiors, fitting light outputs. In turn, it reduces the energy of the building by increasing efficiency.
  • Light meters help in determining exposure in photography. Further, this has a digital computer or an analogue that tells the shutter speed and f-speed. These two factors are crucial for balancing the right exposure for photographers.
  • It comes in use in fields like cinematography to provide intensified lighting.
  • We also use it in areas where very less wastage of light is concerned.
  • In science design, we use it for plants to grow which provide the appropriate lighting. This also happens to avoid outdoor lighting pollution.

Application of Luminance

It plays a significant applicable role in everyday life. If we state it generally, luminance is most exposed on the basis of the whiteness of the screen backdrop it projects on.

Overexposure to it can result in fatal issues of the eyesight. As a result, in the majority of the areas where we use it, its intensity is controlled.

Photography aside, we also use it in TV, computers and other screen projectors.

FAQ on Luminance

Question 1: How do we calculate luminance Ratio?

Answer 1:  We calculate it by using the formula:

LR = L’max/ L’min


L’max =  brightness + the reflected ambient light.

L’min =  black brightness + the reflected ambient light.

Question 2: What is the difference between illumination and luminance?

Answer 2: The luminance is the intensity of light which emits from a unit surface area in a particular direction. Illuminance is the amount of light which projects on a surface.

Question 3: How many lumens is 1 lux?

Answer 3: 1 lux = 1 lumen per sq meter.

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