Light through a window

  1. 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?
     
  2. jcsd
  3. berkeman

    Staff: Mentor

    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...)
     
  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)
     
  5. berkeman

    Staff: Mentor

    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?
     
  6. I dropped him an e-mail and he says to consider it as a sphere.
     
  7. berkeman

    Staff: Mentor

    Okay, so you know what to ratio then?
     
  8. yea.
     
Know someone interested in this topic? Share this thead via email, Google+, Twitter, or Facebook

Have something to add?