"Copy and paste this url:
http://www.geocities.com/womplex_oo1/AgriculturalLights.pdf

It is an examination of the radiation spectra for everything from sunlight in LEO and at ground level, to artificial lights (quite a variety too). Nothing is exact, but I trust these numbers since I did it myself."

Hmm, I'm afraid that does give me much confidence. Though it does seems to somewhat answer my question. It seems plants use the whole visible spectrum, but mostly use around 440 nm and 660nm.

"Visible light consists of radiation from 400-700 nm wavelengths."
"The human eye responds to light with wavelengths from about 790 nm (red) to 430 nm (violet)."
http://katipo.niwa.cri.nz/lauder/uvinfo.htm

I integrated across the spectrum from 10-100,000 nm and discovered that visible light is only about 49% of the total energy density of sunlight."

49% doesn't include the infrared and large percentage is in the infrared.

<snip>
"As for the total energy density I have seen various estimates from 1350 - 1380 watts/sq.meter. I've never seen an estimate over 1400 w/m2 but it may depend on a lot of things, in spite of there being no atmosphere in LEO."

Well the 1418 w/m2 is all radiation from the sun at Earth distance (Space Mission Analysis and Design 3rd ed. pg 454 Table Thermal Data Maximum Solar Radiation Intensity)

<snip>
"Much of what I've studied says that there is negligible difference between the solar spectrum in LEO and the solar spectrum at ground level. It is simply attenuated by the atmosphere."

I agree [except that of the UV light- a large percentage of this light is blocked by our atmosphere (ozone). For instance I don't actually know, but I wouldn't be surprised if there was more UV light on the Mars' surface as compared to Earth's surface even though Mars' total radiation is around 40% of Earth].

"So for ground level you get about 250 watts/m2 total radiation, and 125 watts/m2 visible radiation, roughly. The former is about 18% of the 1366 watts/m2 for low-earth orbit."

You seem to be mixing apples with oranges- 250 w/m2 is not total ground level radiation. Might be about right if you are talking about average yearly total solar radiation you would recieve for a fixed solar panel.