About 7 years ago, I made this growth chamber: In the above image, the top contained five 40 watt T8 fluorescent tubes (Gro-Lux shown here) but, I designed it so that the top can be easily replaced. Inside there was a thermostat that controled 2 exhaust fans on the sides that draw air up through holes on the bottom platform. This growth chamber was run inside a greenhouse from 5 pm to 9 am (16 hrs.). The night temperature inside the greenhouse was typically 65 deg. F. and the light period temperature inside the growth chamber was typically 75 deg. F.. The dark period temperature inside the growth chamber was typically over 90 deg. F.. In 2016, I replaced the top with an LED setup: with ten 8.5 watt 800 lumen warm white bulbs and six "10W" 445nm blue LED chips. The tomato seedlings grew approximately as well as with the fluorescent: In 2017, I replaced the six blue "10W" chips with sixteen 660nm red and ten 430nm blue "3W" chips, but also six 410nm violet chips on just one side to see whether it would make a difference: For the first time, the tomato seedlings grew worse than usual: Although growth was reasonably fast, the leaves were chlorotic and some developed necrotic spots. Compare with day light controls: Some seedlings that I took out early greened up in 3 days under day light. I suspect that the chlorosis was caused by the 660nm LEDs because I also used a spotlight with these LEDs to supplement daylight on a banana plant and it was a lighter green than controls. I don't know whether to blame these particular 660nm LEDs or all 660nm LEDs. This makes no sense to me because Gro-Lux fluorescent has a strong peak at 660nm and there was no chlorosis. If someone wants to test the 660nm LEDs that I used against others, you can buy them here: Hot 50pcs 3W 3Watt deep red 650nm-660nm led chip Plant grow light with 16mm pcb | eBay Incidentally, I didn't see anything unusual about these using a spectroscope. The wavelengths seem to be as advertised.