Let me try to explain another way. You agree adding co2 means the plants can handle more light right?
Why is that?
Because it improves the plants efficiency of photosynthesis (photosynthetic rate)
Now you may see that it improves very minimally in lower light... this is because even mid level lighting is not as efficient as it can be.
Under high light it makes a huge impact on growth... why because the plant is not able to process all of that light and the efficiency of photosynthesis was lower under high light than med light. We are talking efficiency here not growth or energy produced.
Now that's not to say there isn't a net gain there as there is but you are not getting as efficient photosynthetic rates as you do under lower lighting.... this happens up to a point where net photosynthesis will actually go down and the plant needs to slow photosynthetic rates to keep up. So it tacos and other things to reduce light capture. A simple dark period allows this to happen quickly. Under 24 hr light at high intensity it cannot catch up.
So what I'm saying is for those running 24/0 you absolutely cannot run as high of intensity as you can for 16/8 or 18/6.
en.m.wikipedia.org