You choose this size when an 80x80 is marginally too tight and a 100x100 will not fit. The range here is entirely LED, in the 250 to 300 watt class, and that is no accident: over this area the heat from a discharge lamp becomes awkward to remove without your extraction taking over the conversation.
Bars or a panel
From Mars Hydro there are the FC-3000 EVO and FC-E3000 from the bar series, where the light is spread across several bars rather than coming from one point, and the TSW-2000 as a panel. Bars hang closer above the canopy without hot spots, which is decisive in a tent short on height. A panel is more compact and usually cheaper.
Where coverage is stated at this size
The AC Infinity IONFRAME EVO4 at 300 watts states 90x90, exactly this size. The Lux-Helios Pro 240W states 80x80 and 90x90, putting it at the top of its own rating. The Mars Hydro models state no coverage figure on their product pages, so choose those on wattage and fixture shape rather than on a number that is not there.
Your surrounding equipment steps up here
This is the point where the rest of your setup belongs to a 100x100 rather than an 80x80. Budget Ø 125 mm extraction instead of Ø 100 mm, and a second circulation fan below the canopy. The lamp is not what makes this setup dearer.
Efficiency already counts at this scale
A fixture in this class runs thousands of hours, so the difference in micromoles per joule between fixtures of equal wattage comes back on your bill. Lux-Helios puts that figure in the product name; on the other brands it sits on the product page. More on that under LED grow lights.
Frequently asked questions
Can I hang a lamp rated for a larger tent here?
You can, and you will lose light on the walls rather than on your crop. A lamp rated for your size works more efficiently than a larger one hung higher.
Why is there no HPS at this size?
Because the heat over this area is hard to remove without enlarging your extraction considerably. If you want HPS anyway, see MH & HPS and count the cooling in.
Bars or panel?
Bars if you are short on height, because they hang closer without hot spots. A panel if height is not a constraint.
