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Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. [1] In other words, brightness is the perception elicited by the luminance of a visual target. The perception is not linear to luminance, and relies on the context of the viewing environment (for example, see White's illusion).
A luminance meter is a device used in photometry that can measure the luminance in a particular direction and with a particular solid angle. The simplest devices measure the luminance in a single direction while imaging luminance meters measure luminance in a way similar to the way a digital camera records color images.
N bb is a fudge factor that is normally 1; it's only of concern when comparing brightness judgements based on slightly different reference whites. Here Y is the relative luminance compared to white on a scale of 0 to 1 and L A is the average luminance of the adapting visual field as a whole, measured in cd/m 2.
Illuminance diagram with units and terminology. In photometry, illuminance is the total luminous flux incident on a surface, per unit area. [1] It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate with human brightness perception. [2]
The lumen (symbol: lm) is the unit of luminous flux, a measure of the perceived power of visible light emitted by a source, in the International System of Units (SI). ). Luminous flux differs from power (radiant flux), which encompasses all electromagnetic waves emitted, including non-visible ones such as thermal radiation
Prior to the definition of the candela, a variety of units for luminous intensity were used in various countries. These were typically based on the brightness of the flame from a "standard candle" of defined composition, or the brightness of an incandescent filament of specific design.
Luminance for instance is a measure of the density of luminous intensity in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m 2).
Photometry is a branch of optics that deals with measuring light in terms of its perceived brightness to the human eye. [1] It is concerned with quantifying the amount of light that is emitted, transmitted, or received by an object or a system.