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What is Luminance?

What is Luminance?

Ah, the question we all ask when learning about light and colors. “What does luminance mean?”. There are plenty of definitions for the word. But one of the simplest ones is that luminance is how bright an object appears to your eye. For example, when you look at the world around you, without taking note of the colors, you will notice that every object has its degree of luminance and that we live in a luminance kingdom.

Luminance of light is measured by candelas per square meter (cd/m2). It is a property that provides the source light with the strength it displays and the amount that we, humans, can receive. Another excellent example of luminance lighting is what you’re reading right now. You can see white space and black words. But you actually see the luminance of the black words and the luminance of the white spaces.

What we see in our everyday life is luminance. This means that our sources of light, such as the sun or the moon, have luminance. These two light sources give us an excellent idea of the amount of brightness the naked eye can see. It would be best if you didn’t look at the sun for too long because it is incredibly bright, and you get 1,600 cd/m2 into your eye.

In this article, we will discuss:

  • Is luminance similar to illuminance and brightness?
  • What is luminance flux?
  • More about luminance
what is luminance

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Is Luminance Similar to Illuminance and Brightness?

People in the lighting world use several terms that may be confusing, mainly if used interchangeably when they mean different things. It’s easy to confuse these three terms because they sound so similar.

They’re all vital to understanding display calibration, but the terms mean different things. The easiest way to understand the difference between luminance vs. illuminance is to switch on your desk lamp. Now, there are two kinds of light you will notice.

The first thing noticed is the amount of light that passes through the lightbulb. This is luminance. The second kind of light you will notice is what hits the desk. This light is called illuminance. These two kinds of light are both quantifiable, while brightness isn’t. We can only perceive the brightness of light but cannot measure it objectively.

Here are some definitions to help you remember:

Luminance Definition

Referring to the vision we asked you to imagine earlier, luminance is the light reflected from a flat surface. Our eyes can only detect this light from particular angles. Keep in mind that the light reflected on a surface is what allows us to see objects. This light gets into our eyes and allows us to perceive the brightness of a particular object. What we see in our everyday lives is luminance. We can also safely say that every light source we look at also as luminance. We’ve already mentioned that the luminance provided by the sun and moon gives us a vast range of brightness we can handle through the human eye.


Illuminance can also be called incident light. This is the beam of light that touches or lands on the surface. If the illuminated area is closer to the light source, the illuminance will be of high value. It is described as horizontal illuminance if light from the source lands on a horizontal surface such as your kitchen counter or a desk. If it lands on a vertical surface like your bedroom wall, it’s called vertical illuminance.
Illuminance for lighting applications highly depends on how complex a visual task is. For instance, you need a high illuminance value when reading small fonts compared to walking down a hallway.


The intensity of light we perceive with our eyes. Unlike luminance and illuminance, we cannot measure brightness. We can use words such as ‘brilliant or ‘dim’ to describe it. We can also describe it in percentages. Brightness can refer to how much an object is affected by contrast. For example, your laptop screen is much brighter when you look at it in a dark room. However, when you take it outside in the sun, it won’t be as bright.

What is Luminance Flux?

When you’re buying a light bulb, the only thing you mostly think about is how much light it emits. The amount of light a light bulb gives you is called luminous power or luminous flux. Luminous flux measures the amount of visible light that is emitted by the source. It is measured in lumen.

Its brightness usually determines the number of lumens a lighting fixture produces.

But, this doesn’t mean that you should choose a lighting fixture based on its lumen output. Keep in mind that lumens measure the amount of light emitted by a light source. Lumens do not measure the amount of light you perceive with your eye on any application.

You can perceive light on different applications such as a computer, TV, or lighting fixture. When you only consider the lumen output when buying a lighting fixture, you will get an inaccurate view of its performance. Lumen output should never be the reason you determine whether or not a lighting fixture is suitable. You have to measure both luminance and illuminance when evaluating the suitability of a lighting fixture.

More About Luminance

It is Seen by the Human Eye

We see objects due to the amount of light in a space and the reflection of different surfaces in the space. Luminance is all about the light reflected from the surface of an object.

Luminance is Dependent on a Surface

Luminance can only be seen if a surface is present. Remember that different objects have differing refraction or reflection rates, so their luminance is also different. For example, luminance on the surface of your jeans and the surface of your kitchen table is different.

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