Excellent diagrams, 419
I don't really think that the question has been settled on the basis of yield (even without regard to cost). 24/0 increases yield in some crops (e.g., lettuce, peppers) and actually hurts yield in others (e.g., tomatoes). Some crops do benefit from extended daylength, but with no difference in yield between 20/4 and 24/0.
Extended/continuous lighting does generally reduce chlorophyll count, so if very long days do increase growth rate in veg, this may come at a cost to maximum photosynthetic capacity in bloom, and therefore actually hurt yield.
The bottom line is that the impact on
needs to be determined experimentally, and we can expect some variation based on genetics and style of grow. If very long days are beneficial at all, this is only likely to have a noticeable difference for plants that are given a long period of veg (e.g., ScrOG from seed), and not likely to have any measurable impact in a SOG.
penguin