Luminance is a measure of the amount of light emitted or reflected from a surface and seen by an observer. It is expressed in candelas per square meter (cd/m²) and is an important factor in determining how bright or intense an object appears in the context of lighting. Luminance differs from lumen , which measures the total light output of a light source, because luminance specifically relates to how light is perceived on a surface, depending on surface properties (such as color and reflectance) and the viewing angle .

What is luminance?

Luminance describes not only how much light emanates from a source, but also how the light is perceived by an observer. It takes into account the brightness of a surface that reflects or emits light, depending on the incoming light and the reflective properties of that surface.

Luminance is a measure of visual perception of brightness and is strongly influenced by the light falling on a surface , its reflectance , and the angle of observation. Two surfaces that emit the same amount of lumens can have different luminance levels depending on their properties (for example, a black floor reflects less light than a white floor).

How is luminance measured?

Luminance is measured with an instrument called a luminance meter or photometer . This device measures the amount of light emitted by a surface and how much of it is seen from a given viewing angle. The unit for luminance is cd/m² (candela per square meter). The more candelas per square meter, the brighter the surface appears.

• 1 candela (cd) is the luminous intensity of a particular light source in a specific direction.
• 1 square meter (m²) is the area of the object or resource being analyzed.

Example

Imagine you're looking at two screens: an OLED screen and an LCD screen . Although both screens can emit the same amount of light (i.e., they have the same lumens ), the OLED screen will likely have more luminance because it emits direct light rather than reflecting it. This makes the OLED screen appear brighter depending on the viewing angle.

Importance of luminance

1. Visual comfort : Luminance affects the visual comfort of a space. Too much luminance can cause eye strain , while too little luminance can lead to unclear visual perception . Therefore, it's important to find a balance in lighting design, for example, in workspaces and living rooms.
2. Lighting and design : In architecture and interior design, luminance is used to create an optimal visual experience. For example, a monitor viewing area in an office is designed so that the monitor's luminance matches the ambient lighting to prevent glare .
3. Screens and displays : Luminance plays a major role in screen technology. The luminance of a TV or computer screen determines how bright the image appears, which is important in various lighting conditions. It's often adjusted in modern devices to improve visibility, for example, in brightly lit environments.
4. Security and traffic lighting : Luminance is important in public spaces such as streetlights and traffic signs, where it affects visual comfort and visibility for drivers and pedestrians. Insufficient luminance can lead to safety concerns .

Luminance and luminance contrast

Another important aspect of luminance is luminance contrast , which describes the difference in luminance between two areas or objects. In many cases, high luminance contrast is desirable because it helps make objects more visible. Consider, for example, traffic lights, where a high luminance contrast between the green and red lights makes it easy to quickly identify which light is on.

Summary

Luminance is the measure of the amount of light emitted from a surface and visible to an observer, measured in candelas per square meter (cd/m²) . It differs from lumen because lumens measure the total light output of a source, while luminance focuses on how that light is perceived on a specific surface, depending on its reflectance and viewing angle. Luminance is important for visual comfort, lighting design, display technology, and also in public safety applications. It helps determine how bright or visible an object appears in a specific environment.