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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 ( infrared ).
A 230-volt LED filament lamp, with an E27 base. The filaments are visible as the eight yellow vertical lines. An assortment of LED lamps commercially available in 2010: floodlight fixtures (left), reading light (center), household lamps (center right and bottom), and low-power accent light (right) applications An 80W Chips on board (COB) LED module from an industrial light luminaire, thermally ...
Luminous efficacy can be normalized by the maximum possible luminous efficacy to a dimensionless quantity called luminous efficiency.The distinction between efficacy and efficiency is not always carefully maintained in published sources, so it is not uncommon to see "efficiencies" expressed in lumens per watt, or "efficacies" expressed as a percentage.
For example, a 100-watt, 1000 hour, 120-volt lamp will produce about 17.1 lumens per watt. A similar lamp designed for 230 V would produce only around 12.8 lumens per watt, and one designed for 30 volts (train lighting) would produce as much as 19.8 lumens per watt. [76] Lower voltage lamps have a thicker filament, for the same power rating.
Luminous flux (in lumens) is a measure of the total amount of light a lamp puts out. The luminous intensity (in candelas) is a measure of how bright the beam in a particular direction is. If a lamp has a 1 lumen bulb and the optics of the lamp are set up to focus the light evenly into a 1 steradian beam, then the beam would have a luminous ...
The small excess fractional value comes from the slight mismatch between the definition of the lumen and the peak of the luminosity function. The lumen is defined to be unity for a radiant energy of 1/683 W at a frequency of 540 THz , which corresponds to a standard air wavelength of 555.016 nm rather than 555 nm , which is the peak of the ...
If a lamp has a 1 lumen bulb and the optics of the lamp are set up to focus the light evenly into a 1 steradian beam, then the beam would have a luminous intensity of 1 candela. If the optics were changed to concentrate the beam into 1/2 steradian then the source would have a luminous intensity of 2 candela.
The luminous efficacy of a typical CFL is 50–70 lumens per watt (lm/W) and that of a typical incandescent lamp is 10–17 lm/W. [38] Compared to a theoretical 100%-efficient lamp ( 680 lm/W ), CFL lamps have lighting efficiency ranges of 7–10%, [ 39 ] versus 1.5–2.5% [ 40 ] for incandescents.