Zapins· Plant Whisperer
I agree with Hoppy's points. Ultimately several experiments would be needed to figure out exactly the relationship. I'm sure it isn't linear.Someone would need to do the experimenting to be sure, but I'm 90% sure that duration and intensity are not even close to being equivalent. Plants all require a minimum intensity to grow at all, and no matter how long the lights are on if the intensity is below that minimum, the plants don't grow. Also, plants can only use light if they have all of the nutrients needed to grow at the rate appropriate to that light intensity. Adding more light, without those nutrients, all of them, does not cause the plants to grow faster.
But, it is possible that within a small range of intensities, more time can compensate for lower light.
If you make your original question more extreme the answer becomes easier to envision; does exposing the plants to a blindingly bright light for 1 second fulfill their daily light needs? Does exposing plants to a candle light for 24 hours a day allow them to grow and survive?
To some extent plants are able to compensate but not by as much as you'd think. In my experience simply keeping the photoperiod the same or reducing it slightly by an hour or two while doubling the intensity will help plants grow more productively as long as they don't run out of nutrients.