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The former sense is sometimes called luminous efficacy of radiation, [4] and the latter luminous efficacy of a light source [5] or overall luminous efficacy. [ 6 ] [ 7 ] Not all wavelengths of light are equally visible, or equally effective at stimulating human vision, due to the spectral sensitivity of the human eye ; radiation in the infrared ...
Factor ()Multiple Value Item 0 0 lux 0 lux Absolute darkness 10 −4: 100 microlux 100 microlux: Starlight overcast moonless night sky [1]: 140 microlux: Venus at brightest [1]: 200 microlux
In lighting design, the lumen method, (also called zonal cavity method), is a simplified method to calculate the light level in a room. The method is a series of calculations that uses horizontal illuminance criteria to establish a uniform luminaire layout in a space.
At the time the UK established candlepower as a unit, the French standard of light was based on the illumination from a Carcel burner, which defined the illumination that emanates from a lamp burning pure colza oil (obtained from the seed of the plant Brassica campestris) at a defined rate. Ten standard candles equaled about one Carcel burner.
A light bulb, for example, might have 2% efficiency at emitting light yet still be 98% efficient at heating a room (In practice it is nearly 100% efficient at heating a room because the light energy will also be converted to heat eventually, apart from the small fraction that leaves through the windows).
Lumen maintenance is the most useful gauge to determine the lifetime or useful light output rating of an LED light source. Unlike traditional light sources such as incandescent lamps, LEDs rarely fail outright and instead continue to emit light, albeit at slowly diminishing rate over time. [ 1 ]