Light through a window


by bobobano
Tags: light, window
bobobano
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#1
Mar21-11, 03:51 PM
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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berkeman
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#2
Mar21-11, 04:28 PM
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Quote Quote by bobobano View Post
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...)
bobobano
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#3
Mar21-11, 04:41 PM
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)

berkeman
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#4
Mar21-11, 04:50 PM
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Light through a window


Quote Quote by bobobano View Post
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?
bobobano
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#5
Mar21-11, 04:59 PM
P: 4
I dropped him an e-mail and he says to consider it as a sphere.
berkeman
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Mar21-11, 05:04 PM
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Quote Quote by bobobano View Post
I dropped him an e-mail and he says to consider it as a sphere.
Okay, so you know what to ratio then?
bobobano
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#7
Mar21-11, 05:12 PM
P: 4
yea.


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