I wonder if the spectrum is the same for Fulham's 39w bulbs i have?
It says it has 3200 lumens, and that the Midday only has 2400 or something like that.
Would that make a difference in growth speed, or would the spectrum do that mostly?
So you are asking how sheer intensity compares to good spectrum. Which one will result in better plant growth? I don't really know the answer to that. And I am not sure what are we really comparing - a few extra % of efficiency I guess. In the old days we used whatever bulbs we got and I do think we could grow all of today's "rare" plants too IF we added enough intensity. Strong light takes care of it all I guess. How much do we refuse that statement today? Are all these fancy LEDs and what not spectrums really worth it?
Here are a few thoughts I wrote today. They have to do with what you are asking: