Spectral Radiance and it's Units

  • Thread starter Umabel
  • Start date
  • #1
21
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I'm told the spectral radiance of a source is in the following units

W
----------------
cm^2 * sr * nm

And I try to use this to figure the spectral output of monochromator (in W), but I can't seem to cancel out the units. I multiply the spectral radiance by four other terms

slit width (cm)
slit height (cm)
solid angle, using a quick "f-number" equation (sr)
and then the transmission optics factor, which I assume could be unitless but I could be wrong.

Anyways, anybody know why I get W/nm instead of W? Or is it really just W?
 

Answers and Replies

  • #2
253
1
What would be the wavelength of the transmitted light from the monochromator???
 
  • #3
21
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I assume the source is monochromatic here, so the wavelength coming out of monochromator is also monochromatic...let's just say that the radiation is at 400nm or something...
 
  • #4
253
1
So...what happens when you multiply your original equation by the transmitted wavelength??
 
  • #5
21
0
If I multiply the rest of the equation by let's say, 400nm, then the nm units cancel out...

edit: though I have to admit that I am not totally convinced that this is what the unit implies. Is it some invisible reminder that the spectral radiance depends on what wavelength region this source is emitting from?
 
Last edited:

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