Luminous intensity (luminosity, I) Definition:
Point source of light intensity in a certain direction, that is, light emitted per unit time by the amount of light, also referred to as brightness, used in candelas (cd, cd), defined as an international candle made with whale fat candles burn 120 cells per hour cold (grain) issued by the luminosity, a cold frame is equal to 0.0648 g.
Light intensity (brightness) of the unit
Common unit of luminous intensity candela (cd, cd), the international standard candles (lcd) is defined as an ideal blackbody at the freezing point of platinum temperature (1769 ℃), the perpendicular to the blackbody (a surface area of 1m2) direction 60 millionth luminosity, so-called ideal black body is equal to the emissivity of the object, the object of all the radiation energy can be absorbed out, the temperature has been maintained uniform fixed, the international standard candle (candela) with the old standard candle (candle) the exchange relationship 1candela = 0.981candle
Unit of luminous flux and flux
Flux (φ) definition:
Point source or non-point source emitted per unit time in the energy, which can produce a visual person (people can feel out of radiant flux) is called flux.
Unit of luminous flux
Unit of luminous flux in lumens (abbreviated lm), 1 lm (lumen or lm) is defined as an international standard candles light source within the unit solid angle through which the arc flux, because the entire area of the spherical 4πR2, so lumen luminous flux equal to one candela luminous flux emitted by the 1/4π, or that sphere has 4π, so according to the definition we can see a cd lumens point light will radiate 4π lumens, ie φ (lm) = 4πI (candlelight), assuming △ Ω is a small three-dimensional arc angle in △ Ω solid angle flux △ φ, there △ φ = △ ΩI. |
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