Led is already at 2.7 umol/j...... As stated a de hps fixture is at 1.7......
No. The DE is 1.7, the led
can be 2.7. Small difference in words, major difference in reality (requires running many cobs very soft to match hps). Also not denying the numbers itself, never have.
I'm not going to repeat everything I posted in the DE thread, but there's more to a light than umols. As I posted there, the efficiency difference in par light is pretty much all the led fans got. Rhaz even translates par watt directly to gram. While in reality, the par light is not the only type of light affecting photosynthesis rates.
There's really no point in arguing about it, it's a scientific fact that will become more obvious when more people move to led. Yes, even taking the radiation heat into account led CAN still be more efficient, with or without having to raise ambient temp. Everything else being equal, same ppfd, led needs higher ambient temp to result in the same leaf temp and thus same photosynthesis and metabolism rate. This is not an insignificant difference either, upo 20%, evening out the reflector losses. How much exactly doesn't even matter for the simple fact that those par light efficiency numbers obviously do not translate directly to photosynthesis efficiency, and that is the real reason one puts a grow light above plants, not to break efficiency numbers at the source.
If one replaces a 900ppfd hps setup with 900ppfd led, everything else being equal, amd no extreme temps, the hps would result in more photosynthesis. Leaf temp matters... Obviously the spectrum of the led can be more efficient for photosynthesis, more blue and especially red, which makes the white cobs so ironic. The worse the spectrum for photosynthesis, the better for warming plants.
The majority of professional leds in horticulture are not white cobs... The cree cobs are very efficient at producing light, which you guys translate directly to an equal amount in photosynthesis increase, which simply isn't true.
I'd love to see someone add some IR leds to a blurple/white setup... @FanJan?