Hi.

Looking at a graph of light absorption, chlorophyll (a+b) appear to
absorb at a peak of 642 and 662 nm in the red region.

I'd guess that the action-spectrum would show maximum action at some
point between these two wavelengths, however the graph I have shows
the peak activity at around 690nm. What's the deal?

If you had to use a red light with one specific wavelength, what would
it be?

Thanks.