![]() Moonless, overcast night sky ( starlight) Here are some examples of the illuminance provided under various conditions: Thus, lighting a larger area to the same illuminance (lux) requires a greater luminous flux (lumen).Īs with other named SI units, SI prefixes can be used. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. However, the same 1000 lumens spread out over 10 square metres produces a dimmer illuminance of only 100 lux.Īchieving an illuminance of 500 lx might be possible in a home kitchen with a single fluorescent light fixture with an output of 12 000 lumens. One lux is equal to one lumen per square metre:Ī flux of 1000 lumens, spread uniformly over an area of 1 square metre, lights up that square metre with an illuminance of 1000 lux. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance is inversely proportional to area when the luminous flux is held constant. One can think of luminous flux (with the unit lumen) as a measure of the total "amount" of visible light present, and the illuminance as a measure of the intensity of illumination on a surface. Illuminance is a measure of how much luminous flux is spread over a given area. The word is derived from the Latin word for "light", lux.Įxplanation Illuminance In English, "lux" is used as both the singular and plural form. ![]() It is analogous to the radiometric unit watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a model of human visual brightness perception, standardized by the CIE and ISO. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. ![]() It is equal to one lumen per square metre. The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI).
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