growing crops under artificial lighting

I'm getting tired of the widely-repeated claim that it is impractical to
grow crops under artificial light (particularly if your power source is
solar). It just doesn't make sense, for two reasons. First, if your
solar power plant is in orbit where it receives sunlight 24/7, you've
already got about seven times as much sunlight to start with as a field
on Earth. Second, though there are losses in converting the sunlight to
electricity and back to light, you can make the light you convert it to
be 100% pure clorophyll-absorbed prime wavelength, whereas the light
that falls on Earth is mostly wavelengths that plants can't use anyway.

Put those factors together, and I suspect that a km^2 of solar cells (or
similar solar power collector area) could grow MORE than one km^2 of
crops.

But suspicions aren't worth much; I really need some numbers. And here
my ignorance is getting in the way, and I'd like to correct that.
Can anyone point me to sources of data on absorption spectra for
important crop species, etc.?

I've started googling but have turned up surprisingly little so far.
(E.g., I know the difference between chlorophyll A and B, but I have no
info on what the relative balance between them is for any relevant
plant.)

Thanks,
- Joe

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