Not on light, but on Soya Beans:
There was a peper in American Bee Journals some years ago on the
topic. The up-shot...some varieties show better yields when honey-
bees are present in the fields, others don't. My work on cv. Maple
Arrow in Ontario showed the latter result. The work in ABJ was, I
seem to remember, authored by Martin. I may be able to come up
with a citation, but right now lots of my files are packed away
after a building move. The literature in general indicates that
honeybees are not needed (I suspect this generalization to be
correct, but with lots of exceptions) as is indicated by Free (1970)
and McGregor (1976). Do you know these encyclopaedic works..Free,J.B.
Insect Pollination of Crops, Acvademic Press.; McGregor, S. E. 1976
USDA Handbook ? exact title but Insect Pollination of Cultivated
Crop Plants rings  a bell.
I hope this helps a bit. Cheers, Peter Kevan, U of Guelph.