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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 ...
Light with the same radiant intensity at other wavelengths has a lower luminous intensity. The curve which represents the response of the human eye to light is a defined standard function y (λ) or V (λ) established by the International Commission on Illumination (CIE, for Commission Internationale de l'Éclairage ) and standardized in ...
Several measures of light are commonly known as intensity: Radiant intensity , a radiometric quantity measured in watts per steradian (W/sr) Luminous intensity , a photometric quantity measured in lumens per steradian (lm/sr), or candela (cd)
Fluorescent lamps in various embodiments. Since their introduction as a commercial product in 1939, many different types of fluorescent lamp have been introduced. Systematic nomenclature identifies mass-market lamps as to overall shape, power rating, length, color, and other electrical and illuminating characteristics.
See Lumen/FT2. Footlambert (FL) A unit of luminance equal to 1 / ? candela per square foot or to the uniform luminance at a perfectly diffusing surface emitting or reflecting light at the rate of one lumen per square foot. A lumen per square foot is a unit of incident light and a footlambert is a unit of emitted or reflected light.
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 ).
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
Light whose wavelength is well outside the visible spectrum has a luminous energy of zero, regardless of the amount of radiant energy present. The SI unit of luminous energy is the lumen second , which is unofficially known as the "talbot" in honor of William Henry Fox Talbot .