GC: n
CT: Luminous flux is energy.The energy is the total amount of light energy radiated from a light source in all directions. The luminous flux is measured in lumens and is the parameter used to describe the “brightness” of a projector.
One lumen is the Luminous Flux or expressed more simply, the total amount of light energy emitted into one solid angle or steradian (see definition below), by a point source having a luminous intensity of 1 candela.
One steradian solid angle is the three dimensional angle with its vertex in the centre of a sphere which covers ¼p of the surface of the sphere. If we place a point light source with the luminous intensity of 1 candela at the centre of the sphere and measure the light being emitted into one steradian, we get 1 Lumen.
The lumens value for projectors describes its luminous flux – or the total amount of light energy emitted from the lens.
S: http://www.dnp-screens.com/DNP08/Technology/Basic-Visual/What-is-light/Luminous-flux.aspx (last access: 12 December 2014)
N: 1. luminous (adj): early 15c., “full of light,” from Latin luminosus “shining, full of light,” from lumen (genitive luminis) “light,” related to lucere “to shine”. Related: Luminously.
flux (n): late 14c., “abnormally copious flow,” from Old French flus “a flowing, a rolling; a bleeding” (Modern French flux), or directly from Latin fluxus (adj.) “flowing, loose, slack,” past participle of fluere “to flow”. Originally “excessive flow” (of blood or excrement), it also was an early name for “dysentery;” sense of “continuous succession of changes” is first recorded 1620s. The verb is early 15c., from the noun.
2. The amount of light radiated or emitted by a source, measured in lumens.
3. The radiant power is the total radiated power in watts, also called radiant flux. This power must be factored by the sensitivity of the human eye to determine luminous flux in lumens.
4. The lumen is the standard unit for the luminous flux of a light source. It is an SI derived unit based on the candela. It can be defined as the luminous flux emitted into unit solid angle (1 sr) by an isotropic point source having a luminous intensity of 1 candela. The unit lumen is then equal to cd x sr.
S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=luminous&searchmode=none; http://www.etymonline.com/index.php?allowed_in_frame=0&search=flux&searchmode=none (last access: 12 December 2014). 2. TERMIUM PLUS (last access: 12 December 2014). 3 & 4. http://hyperphysics.phy-astr.gsu.edu/hbase/vision/lumpow.html (last access: 12 December 2014).
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