luminous energy

Dictionary: luminous energy

n.
The radiant energy of electromagnetic waves in the visible portion of the electromagnetic spectrum.

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The radiant energy in the visible region or quantity of light. It is in the form of electromagnetic waves, and since the visible region is commonly taken as extending 380–760 nanometers in wavelength, the luminous energy is contained within that region. It is equal to the time integral of the production of the luminous flux. See also Photometry.

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The time integral of luminous flux; given by the product of the luminous flux and the time that the flux is maintained, if the luminous flux is of constant value; usually expressed in lumen-hours.

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Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: the energy associated with visible light

Wikipedia: Luminous energy

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In photometry, luminous energy is the perceived energy of light. This is sometimes also called the quantity of light.

Luminous energy is not the same as the radiant energy, the corresponding objective physical quantity. This is because the human eye can only see light in the visible spectrum and has different sensitivities to light of different wavelengths within the spectrum. When adapted for bright conditions (photopic vision), the eye is most sensitive to light at a wavelength of 555 nm. Light with the same power at longer or shorter wavelengths has a lower luminous energy.

Units

The SI unit of luminous energy is the lumen second, which is unofficially known as the Talbot in honor of William Henry Fox Talbot.

In other systems of units, luminous energy may be expressed in basic units of energy.

Quantity	Symbol	SI unit	Abbr.	Notes
Luminous energy	Q_v	lumen second	lm·s	units are sometimes called talbots
Luminous flux	F	lumen (= cd·sr)	lm	also called luminous power
Luminous intensity	I_v	candela (= lm/sr)	cd	an SI base unit
Luminance	L_v	candela per square metre	cd/m²	units are sometimes called "nits"
Illuminance	E_v	lux (= lm/m²)	lx	Used for light incident on a surface
Luminous emittance	M_v	lux (= lm/m²)	lx	Used for light emitted from a surface
Luminous efficacy		lumen per watt	lm/W	ratio of luminous flux to radiant flux
SI • Photometry

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	talbot (optics)
	lumberg (optics)
	lumen-hour (optics)

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		Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more
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