Luminance

What does Luminance mean?

Luminance is a measure of the intensity of light per unit solid angle that a surface emits or reflects in a given direction. It is a photometric quantity that describes the brightness of a light source or a surface as perceived by the human eye. Luminance is closely related to the concept of luminous intensity, which measures the total amount of light emitted by a source in all directions. However, while luminous intensity is a measure of the total output of light, luminance is a measure of the intensity per unit solid angle and therefore describes the brightness in a specific direction.

Luminance is measured in units of candelas per square Meter (cd/m2). The candela is the SI unit of luminous intensity and is defined as the luminous intensity, in the direction of the normal, of a full radiator at the freezing point of platinum. Luminance can also be expressed in units of Foot-lamberts (fL), which are commonly used in the lighting industry. One foot-lambert is Equal to 3.426 cd/m2.

Applications

Luminance plays an important role in many areas of technology, including:

1. Lighting design: Luminance is a key factor in the design of lighting systems, as it determines the perceived brightness of a space. Lighting designers use luminance measurements to create uniform and comfortable lighting conditions.
2. Photography and imaging: Luminance is a critical factor in determining the exposure and contrast of a photograph or image. Photographers use luminance meters to measure the brightness of a scene and adjust the camera settings accordingly.
3. Display technology: Luminance is an important factor in the quality of displays, as it determines the brightness and contrast of the images displayed. Display manufacturers use luminance measurements to calibrate and optimize their displays.
4. Medical imaging: Luminance is used in medical imaging techniques, such as ultrasound and X-rays, to visualize and diagnose medical conditions.
5. Automotive lighting: Luminance is a critical factor in the design of automotive lighting systems, as it determines the visibility and safety of vehicles on the road.

History

The concept of luminance has been studied and developed over many centuries. In the 16th century, Italian mathematician and astronomer Giovanni Battista della Porta developed the camera obscura, a device that used a lens to project an image of the outside world onto a screen. The camera obscura demonstrated the principles of perspective and luminance, and it was used by artists to create realistic paintings.

In the 18th century, English scientist Isaac Newton conducted experiments on the nature of light and color. Newton’s work laid the foundation for the development of photometry, the science of measuring light. In the 19th century, German physicist Hermann von Helmholtz developed the First luminance meter, which allowed scientists to measure the brightness of light sources.

In the 20th century, the development of electric lighting led to a renewed interest in luminance. Lighting engineers used luminance measurements to design lighting systems that met the needs of human vision. Today, luminance is an essential tool in many areas of technology, including lighting design, photography, display technology, medical imaging, and automotive lighting.