![]() ![]() Chapter 9 – Rules and Style Conventions for Spelling Unit Names, National Institute of Standards and Technology.Ĭurrently, we have around 5661 calculators, conversion tables and usefull online tools and software features for students, teaching and teachers, designers and simply for everyone. International Electrotechnical Commission. Lighting / Radiation, quantities and units. SI Derived Units, National Institute of Standards and Technology. One watt is also defined as the current flow of one ampere with voltage of one volt. One watt is defined as the energy consumption rate of one joule per second. The watt unit is named after James Watt, the inventor of the steam engine. 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. Lumens per watt (lm/W) divided by the surface area A in square meters (m 2):Į v(lx) = P (W) × η (lm/W) / A (m2 ) Lux definition The illuminance E v in lux (lx) is equal to the power P in watts (W), times the luminous efficacy η in In lumens per watt (lm/W) divided by the surface area A in square feet (ft 2):Į v(lx) = 10.76391 × P (W) × η (lm/W) / A (ft2 ) Watts to lux calculation with area in square meters The illuminance E v in lux (lx) is equal to 10.76391 times the power P in watts (W), times the luminous efficacy η Watts to lux calculation formula Watts to lux calculation with area in square feet ![]() * the predefined luminous efficacy values are typical / average values.
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