Hi all,
It is quite a complex relationship, every plant will have a unique "compensation point". The compensation point is the amount of light intensity (on the light curve) where the rate of photosynthesis exactly matches the rate of respiration.
Below this point the plant will not grow and will lose biomass, before eventually dying.
This is why a longer period of lower intensity light may not compensate for a shorter period of high intensity light.
Once you are past the compensation point the various photosynthetic pathways will react in different ways to the incident light energy.
Photosynthesis is a complex process, if you think of it like a conveyor belt in a manufacturing process, the photosynthetic rate is constrained by whatever component is in shortest supply. To use a motor car analogy you may be able to screw the doors on a car very quickly (or add light photons), but if it takes a minimum of 5 minutes to install the transmission (or for enough CO2 to diffuse in through the leaf stomata) an increase in the "door screwing rate" is irrelevant.
Your best bet is to have a look through the old posts, as you will find a lot of discussion on the "light - fertiliser - CO2" relationship, and what happens when it is out of balance.
cheers Darrel
