Look at the differing blues in these pics.
Which spectrum is best for flowering?
Confused.com lol
Hlg Diablo
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Hlg Scorpion
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Hlg blackbird
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Scorpion B spec
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GLA
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Lumatek Attis
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Mars hydro
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"best" is a word that's, usually speaking, "best" avoided because, one, it's not defined and, since it's not defined, defining what "best" means that defining it can become the focus of the discussion rather answering the question.
The Grow Lights Australia spectrum looks excellent as an all round spectrum. I first saw that maybe two years ago and was really impressed - it certainly covers the bases in terms of providing light in the ePAR range so congrats to GLA for pushing the envelope in that respect. By that I mean that I haven't seen any other light vendor do anything like GLA in terms of incorporating different wavelengths to their fixtures. It's a risk - research cost and for "straying outside the markers" in terms of spectrum - but they took the leap.
Back to the "best" flower spectrum. HLG uses "R" to denote a flower spectrum with the heavy red component while their "B" lights are so labeled because of the heavy blue weighting and those are labeled for using during veg. The lights from Lumatek and Mars are variations on a balanced spectrum. The Diablo looks to be a "balanced" spectrum. Setting those aside, I like the Scorpion because it has incorporated some red in the 730 range but the spectrum from either the Scorpion or the Diablo would be my pick.
IRL, what is my pick?
I went with lights with the spectra shown below and things have worked out well. Chilled (Growcraft) and HLG are the only companies that I know of that make separate veg and flower lights. HLG products never did anything for me - board light with a monster hot spot - so I went with Growcraft*.
Interestingly, the folks at GrowLightScience thought so highly of the flower spectrum for the Growcraft that they have decided to create a vey similar spectrum across their entire product line.
One of the mods at a site that's dedicated to autoflowers (I'm assuming I can't post the name), uses the Growcraft flower light + a Rapid LED blue puck through the entire grow and gets excellent results.
*My veg light only has two light bars so I use a Vipar XS 1500 (not the Pro) and a Rapid LED blue puck in seedling and flower and will use he XS 1500 and a Mars SP 3000 throughout the grow to add spot lighting. For one grow, I ended up with 450-500 watts lighting the grow (in a 2' x 4') but it was a very large plant that yielded something like 880 gm/m2.