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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.
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 ).
Standard incandescent lamps have an efficacy of 10-17 lumens per watts and a lifetime of 750–2500 hours. Tungsten halogen lamps have an efficacy of 12-22 lumens per watts and a lifetime of 2000–4000 hours. Finally reflector lamps have an efficacy of 12-19 lumens per watts and a lifetime of 2000–3000 hours. [2]
A CFL will thrive in areas that have good airflow, such as in a table lamp. ... 4000—4100 250—243 ... The luminous efficacy of lamps is the number of lumens ...
To help compare different orders of magnitude, the following list describes various source in lux, which is a lumen per square metre. Factor Multiple Value
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 ...