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Luminous intensity, a photometric quantity measured in lumens per steradian (lm/sr), or candela (cd) Irradiance, a radiometric quantity, measured in watts per square meter (W/m 2) Intensity (physics), the name for irradiance used in other branches of physics (W/m 2) Radiance, commonly called "intensity" in astronomy and astrophysics (W·sr −1 ...
In physics and many other areas of science and engineering the intensity or flux of radiant energy is the power ... the equation becomes ... c is the speed of light ...
Defining equation SI units ... Irradiance, light intensity ... The Cambridge Handbook of Physics Formulas. Cambridge University Press.
Luminous intensity is the perceived power per unit solid angle. 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 intensity of 1 candela. If the optics were changed to concentrate the beam into 1/2 steradian then the source would have a ...
German astronomer Johannes Kepler discussed the inverse-square law and how it affects the intensity of light. In proposition 9 of Book 1 in his book Ad Vitellionem paralipomena, quibus astronomiae pars optica traditur (1604), the astronomer Johannes Kepler argued that the spreading of light from a point source obeys an inverse square law: [15] [16]
The cosine values may be saved and used in the Fresnel equations for working out the intensity of the resulting rays. Total internal reflection is indicated by a negative radicand in the equation for cos θ 2 {\displaystyle \cos \theta _{2}} , which can only happen for rays crossing into a less-dense medium ( n 2 < n 1 {\displaystyle n_{2 ...
When light strikes the interface between a medium with refractive index n 1 and a second medium with refractive index n 2, both reflection and refraction of the light may occur. The Fresnel equations give the ratio of the reflected wave's electric field to the incident wave's electric field, and the ratio of the transmitted wave's electric ...
The intensity of the light emitted from the blackbody surface is given by Planck's law, (,) = / (), where I ( ν , T ) {\displaystyle I(\nu ,T)} is the amount of power per unit surface area per unit solid angle per unit frequency emitted at a frequency ν {\displaystyle \nu } by a black body at temperature T .