Based on the spectral graphs, I'd go with the Grow Light Science 640. Both lights have a good warranty, but only the GLS 640 tells that it contains Samsung and Osram Diodes, no info on what diodes. If I had to pick between the two, I'd go with the more red spectrum.

I debated on the progrow 640 and the FL1 A few months back, both I think are good lights ultimately I went with progrow. there were a few things I considered cost, spectrum and customer service.

1. cost prowgrow 640 $420 plus tax
Fl1 $450 plus tax and shipping Volt does not offer free shipping and it's pricey over $50.
2. progrow IMO has a better spectrum especially for flower.
3. customer service is both good someone answers the phone when you call. when I called Grow light science Kevin the owner answered the phone, that to me was a green light sealed the deal for me. I was glad I waited a couple weeks to buy the light saved $300

I am not sure what brand diodes are used on the prowgrow. on ledgrowlightsdepot.com they say Samsung and Osram I saw somewhere I can't remember where they were Samsung and Ledestar

as for the Volt Fl1 they use Samsung LM301Z and Osram from the research I have done.

currently I am waiting on my seedlings to get bigger before i put the 640 on them I had to reset my entire grow due to powdery mildew I shit canned every thing clones, 2 mothers. I can deal with spider mites but I wont deal with powdery mildew cleaned out the room with a heavy dose of bleach. the only thing I did was test the light for function. power draw @ max was 637 watts also the light works with AC Infinity controller 69 pro.
ILGM Has a topic on this light with good pics of flower it's title is Grow light search. just google grow light science progrow 640 review and look for I love growing marijuana.

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