Luminance

Luminance is the luminous flux per unit solid angle emitted or reflected from a surface. It is typically denoted by the symbol “L”. The formula for luminance is derived from the ratio of luminous flux to the product of projected area and solid angle. This core formula is expressed as follows:

Here, dφ represents the luminous flux in lumens (lm), dA is the differential area in square meters (m²), dω is the differential solid angle in steradians (sr), and θ stands for the angle between the normal to the surface and the line of sight.

A widely used unit of luminance is candela per square meter (cd/m²) in the SI System. This unit is fundamental, expressing luminance as the amount of light emitted or reflected from each square meter of the surface. The nit (nt) is a non-SI name also used for this unit (1 nt = 1 cd/m²).

Real-world examples showcasing varying luminance values are abundant. For instance, a typical computer monitor might have a luminance of around 250 to 350 cd/m², ensuring a bright and clear display for various tasks. In contrast, a brightly lit outdoor scene could reach luminance values of several thousand cd/m² due to natural sunlight.

Light meters are pivotal in measuring luminance, serving as indispensable tools across various industries. These devices, equipped with photodiodes or photovoltaic cells, quantify the intensity of light falling onto their surface. Their primary functionality lies in capturing and converting light energy into electrical signals, which are then translated into readable units of luminance. Light meters are designed to factor in human perceptibility, accounting for the human eye sensitivity across different wavelengths of light.

Their usage in determining luminance spans diverse fields, including photography, cinematography, and architectural design. Light meters achieve optimal exposure settings in photography and cinematography, ensuring that the captured images or footage exhibit accurate brightness levels and desired contrasts. They enable precise adjustments of aperture, shutter speed, and ISO sensitivity to achieve the desired luminance, influencing the captured scene’s overall mood and visual impact.

Luminance and brightness, often used interchangeably, distinguish how we perceive light. Luminance refers to the amount of light emitted or reflected per unit area from a surface. It focuses on the objective measurement of light intensity and is closely tied to the physical characteristics of a surface. In contrast, brightness encompasses a broader, subjective aspect of how intense or vivid the light appears to an observer.

Luminance is essential in many industries because it affects how we see light. Things like TVs and digital screens must have the right amount of luminance so that what we see is bright, clear, and easy on our eyes. In photography and movies, playing with luminance helps creators make stunning visuals by controlling how light and darkness look. It lets them create different feelings or make certain things stand out in a picture or scene. Luminance is a big deal in different jobs because it shapes how we see and use light daily.