# Light through a window

by bobobano
Tags: light, window
 P: 4 1. The problem statement, all variables and given/known data A lamp producing 1600 lumens is 16" away from a window of 0.015m^2 on a wall 0.14m^2, what is the amount of light through the window. 2. Relevant equations lux = lumens/m^2 3. The attempt at a solution Since there's no material in the window, shouldn't it be the full 1600 lumens seen inside?
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P: 41,369
 Quote by bobobano 1. The problem statement, all variables and given/known data A lamp producing 1600 lumens is 16" away from a window of 0.015m^2 on a wall 0.14m^2, what is the amount of light through the window. 2. Relevant equations lux = lumens/m^2 3. The attempt at a solution Since there's no material in the window, shouldn't it be the full 1600 lumens seen inside?
Welcome to the PF.

I think the point of the question is that the light source is isotropic, so only a fraction of the total light goes through the area of the window. How can you calculate the fraction of the total area that the window represents (hint -- use the distance to the window for something...)
 P: 4 am I correct in thinking that if I multiply the lux over the area, from the lamp to the window, by the window's area I'll get the lumens through the window? Light through window = (light from lamp)/(pi*distance2)*(window surface area)
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P: 41,369
Light through a window

 Quote by bobobano am I correct in thinking that if I multiply the lux over the area, from the lamp to the window, by the window's area I'll get the lumens through the window? Light through window = (light from lamp)/(pi*distance2)*(window surface area)
It is some area ratio, but on re-reading the question, maybe the light source is not isotropic? They mention a wall and a window, so I'm not sure whether to ratio the area of the window to the wall or to an isotropic sphere. Is there a picture that goes with the question, or else are you able to understand the question well enough to answer it now?
 P: 4 I dropped him an e-mail and he says to consider it as a sphere.
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P: 41,369
 Quote by bobobano I dropped him an e-mail and he says to consider it as a sphere.
Okay, so you know what to ratio then?
 P: 4 yea.

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