I don't trust that 120W input power number listed on the Amazon page for the Vivosun. The Vivosun page doesn't actually list the electrical wattage. Most COB assemblies I've seen are usually 50-65W each, and that has six of them plus ~80 normal LEDs. It seems more like ~400W+ input power - so, too much light / heat for your space.
The Mars FC-3000 / FCE-3000 (the smallest in those series) both look like they'd be too (physically) big for a 20x36 area. The smaller of the two (FC-3000) is 22.8" x 20.4". But, if you can squeeze that in, I'd probably recommend it.
Overall, 20"x36" is an odd / non-standard size for a grow area - so it may be hard to find a single light that will provide decent coverage for that space. If you look at the PPFD maps for most lights (not the PPFD vs. height diagrams, which only gives the max peak PPFD at the center), then most lights fall off pretty significantly near the edges (so some coverage areas listed by vendors may not be too realistic). Ultimately, your odd size area may be the reason to go for two smaller lights to even out the coverage. If so, two Mars SP-150's side-by-side might be a good setup for you.
The Mars FC-3000 / FCE-3000 (the smallest in those series) both look like they'd be too (physically) big for a 20x36 area. The smaller of the two (FC-3000) is 22.8" x 20.4". But, if you can squeeze that in, I'd probably recommend it.
Overall, 20"x36" is an odd / non-standard size for a grow area - so it may be hard to find a single light that will provide decent coverage for that space. If you look at the PPFD maps for most lights (not the PPFD vs. height diagrams, which only gives the max peak PPFD at the center), then most lights fall off pretty significantly near the edges (so some coverage areas listed by vendors may not be too realistic). Ultimately, your odd size area may be the reason to go for two smaller lights to even out the coverage. If so, two Mars SP-150's side-by-side might be a good setup for you.