[Laser] Voice communication using 940nm IR LED in full daylight

[Tim Toast]

hi Stuart,

Here is a very large atlas of IR absorption spectra:

http://nldr.library.ucar.edu/collections/technotes/asset-000-000-000-650.pdf

scroll down to the bottom for the graphs. Unfortunately it is in
Inverse Centimeters instead of Wavelength but you can convert one
to the other easy enough i think. Compare with some lower res graphs 
to see if you have it right. 
Also there is some atmospheric emission (google airglow) at some
wavelengths that might cause trouble and more noise but it is small
amounts i think.
I found a graph that had 940nm on it and there were some absorption
lines there but the graph wasn't high res enough to see the exact
wavelengths very well:
http://www.gemini.edu/sciops/ObsProcess/obsConstraints/atm-models/transam1.gif
At 910nm it is near 95 percent transmission. At 940nm it could be 
as little as 70 percent or as much as 95 percent depending on the 
exact wavelength and water vapor content etc... Maybe 850nm is in 
a window instead of in a forest of lines.

hope this helps :)

-toast