1. Luminance describes apparent brightness in a direction

In photometry, luminance measures the light emitted, transmitted, or reflected by a surface per unit projected area in a given direction. It quantifies the brightness of what we see.

2. The SI unit of luminance is candela per square meter

Its symbol is cd/m². This unit is also commonly called a nit, especially when discussing televisions, computer monitors, and smartphone screens.

3. Screen luminance affects viewing comfort

A screen with higher luminance can be easier to see in bright surroundings. However, maximum brightness is not always best: the ideal setting depends on ambient lighting and viewing conditions.

4. Surface finish affects luminance

A glossy surface may reflect light strongly in one direction, creating a bright highlight. A matte surface usually spreads reflected light over a wider range of directions.

5. The Moon shines by reflecting sunlight

The Moon is not a self-luminous light source like the Sun. Its visible surface reflects sunlight, producing luminance that allows us to see it at night.

6. Projector screens have luminance too

A cinema screen reflects light from a projector toward viewers. The screen's material, gain, viewing angle, and room lighting influence the luminance seen by the audience.

7. Luminance is different from illuminance

Luminance describes light leaving or passing through a surface in a particular direction. Illuminance measures how much luminous flux falls onto a surface and is measured in lux.

8. Luminance helps astronomers study the sky

Astronomers use surface brightness and related measurements to study extended objects such as nebulae and galaxies. The luminance of a source is distinct from its total apparent brightness, which also depends on its apparent size.

9. High luminance can cause glare

Extremely bright sources against a darker background can cause discomfort or reduce visibility. Lighting designers consider luminance contrasts when planning roads, offices, and public spaces.

10. HDR displays use high luminance for bright highlights

High Dynamic Range (HDR) content can represent intense highlights alongside dark regions. A display's peak luminance is one factor that influences how effectively it reproduces these bright details.

11. A small source can have high luminance

A tiny LED can look intensely bright even though it emits less total light than a large light source. Luminance depends on the source's projected area and directional light intensity, not simply its total output.

12. Luminance can be measured with specialized instruments

A luminance meter or imaging photometer measures luminance in cd/m². These instruments are used to test displays, lighting systems, vehicle lamps, and other illuminated surfaces.

13. Luminance depends on both the surface and the light

A white wall generally appears brighter under stronger illumination than under dim light. Its luminance also depends on its reflective properties and the direction from which it is viewed.

14. Perceived brightness is not the same as luminance

Human vision adapts to surrounding light and responds to contrast. Two regions with the same physical luminance can appear different depending on their surroundings and viewing conditions.

15. Luminance is important in architectural design

Architects and lighting engineers balance surface luminance, contrast, and glare to make spaces comfortable, readable, and visually appealing.