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A light source with a candle worth of power produces ________.
one lumen / watt
one lumen / meter
one lumen / radian
one lumen / steradian
one lumen / steradian
Luminous intensity is defined as the luminous flux emitted per unit solid angle in a given direction. Since one candela represents one lumen per steradian (1┬аcd=1┬аlm/sr), a light source with a candle worth of power produces one lumen per steradian.
SI Brochure: The International System of Units (SI), Section 2.3.1
Luminous intensity is defined as the luminous flux emitted per unit solid angle in a given direction. Since one candela represents one lumen per steradian (1┬аcd=1┬аlm/sr), a light source with a candle worth of power produces one lumen per steradian.
I=╬й╬жтАЛ тАФ where I is luminous intensity in candela, ╬ж is luminous flux in lumen, and ╬й is solid angle in steradian.
The luminous intensity (I) is measured in candelas (cd). It relates the total luminous flux (Phi) to the solid angle (Omega) into which the light is emitted. The relation is expressed as I=d╬йd╬жтАЛ.
Candela is an SI base unit.
The solid angle is measured in steradians (sr).
One steradian is the solid angle subtended at the center of a sphere by an area on its surface equal to the square of its radius.
Provides a standardized way to measure directed light output.
Independent of distance due to solid angle normalization.
Only defines intensity in a specific direction.
Does not account for spectral sensitivity variations unless photopic vision is assumed.
Light fixture design and photometric evaluation.
Calibration of light meters and sensors.
Lumen/watt is a unit of Luminous Efficacy.
Lumen/meter and Lumen/radian are not standard SI units for light source power distribution.
D is correct тАФ a light source with one candle worth of power, by definition, emits a luminous intensity of one lumen per steradian.
Remember that intensity is directed (per steradian) whereas total flux (lumens) is the sum over all angles.
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