The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total quantity of visible light emitted by a source per unit of time. Thus, lighting a larger area to the same level of lux requires a greater number of lumens.Īs with other SI units, SI prefixes can be used, for example a kilolux (klx) is 1000 lux. 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 lux might be possible in a home kitchen with a single fluorescent light fixture with an output of 12000 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 (measured in lumens) 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. 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 standardized model of human visual brightness perception. 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 SI derived unit of illuminance, measuring luminous flux per unit area. In lumens (lm) divided by 4 times pi times the squared sphere radius r in meters (m): The illuminance E v in lux (lx) is equal to the In lumens (lm) divided by the surface area A in square meters (m 2): The illuminance E v in lux (lx) is equal to the luminous flux Φ V (4⋅π⋅ r (ft) 2) Calculation with area in square meters In lumens (lm) divided by 4 times pi times the squared sphere radius r in feet (ft): In lumens (lm) divided by the surface area A in square feet (ft 2): The illuminance E v in lux (lx) is equal to 10.76391 times the luminous flux Φ V Lumens to lux calculation formula Calculation with area in square feet
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