Luminance - definition
Luminance - definition
Luminance is a physical photometric quantity describing the intensity of light emitted, reflected or transmitted by a surface in a given direction, related to a unit area of that surface and the solid angle of observation. It is measured in candela per square metre (cd/m²) and reflects the subjectively perceived brightness of a surface by the observer.
Unlike luminous flux or illuminance, luminance takes into account the directionality of light emission and its spatial distribution, which makes it particularly important in the analysis of visual experience and visual ergonomics. It is a directional quantity, meaning that it depends on the angle at which a surface is observed, as well as the nature of its structure - e.g. matt, glossy or transparent.
Luminance is used in the design of lighting, displays, screens and the optics of vision systems, where it is important to control and assess the level of brightness of individual scene elements. In screen technology, it is used to define image parameters such as contrast and legibility under different lighting conditions. It is also a key parameter in the analysis of visual comfort and eye protection, e.g. when assessing glare in office spaces.
Luminance measurements use specialised instruments - luminance meters - that measure the amount of light falling on an optical transducer in a specific field of view. Modern measurement methods make it possible to analyse the distribution of luminance over large areas with high accuracy, which is important in the design of public spaces, road infrastructure, as well as in the automotive and aerospace industries.
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