You can find details of photosynthetic perfomance of cannabis at varying irradiance, temperature and CO2 levels in the study "Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions", by Suman Chandra, Hemant Lata, Ikhlas A. Khan and Mahmoud A. Elsohly. Its a very complete study, again with the limitation of studying responses on the short term, and not on after long term acclimatation.

The study reveals that cannabis can handle very efficiently up to 500-600 uE/m2 at ambient CO2, with optimal day temperature near 30ºC (but strongly dropping over it!), and the best range being 25-30ºC. There is no clear photoinhibition point, with photosynthesis still increasing (although little) at 1500 uE/m2 (not at low temps), so that point at optimal temps and ambient CO2 is over that figure

You must take into account than that 7% of margin error refers to white lights sources, broad band ones with limits on the saturation of a given waveband.

On the LED growing research, we are working with relative narrow wavebands strongly saturated, in the look for the highest photosynthesis but accomplishing the most positive sinergies, trying to achieve way highest photosynthetic efficacies than a white light can do.

We are actually getting very nice enhancements on the spectral efficacy (yield/mol of photons PAR) using this approach when refered to white light sources, of near 200%. So its possible to go way ahead. Its not exactly photosynthetic response, but how carbon efficiently fixation is used, that is related to more factors. But the difference is so huge that sure that a significant part is achieved by enhanced photosynthetic response.

A group of grower are performing experiments with standarized measurements in order to find the optimal spectrums (different according to irradiance used?) for cannabis. If you want to join us, you are welcome. Stadistical analysis of experiments may strongly fasten the research, so sharing our results benefits all.