Exactly one square metre is what manufacturers tune their specifications to, so there is least arithmetic for you here. A lamp that says it suits 1 by 1 metre means this space. Budget roughly 300 watts of LED or a 600 watt discharge lamp, and pay attention above all to the coverage stated on the product page.
The LED choice is widest here
The Lumatek ATS 300W Pro states 100x100 explicitly and is passively cooled, so silent. The Lux-Helios LED 300W states the same size and gives 2.8 µmol/J with it, making it the only one here that pins down both coverage and efficiency. From Mars Hydro there are the FC-4800 EVO and FC-E4800 from the bar series, plus the Spectrabox UFO 200W and the ViparSpectra KS3000 at 320 watts.
Discharge at the classic size
Fertraso and Sylvania both supply 400 and 600 watts, and Fertraso the 400 watt HPIT metal halide besides for the growth phase. Six hundred watts of HPS over a square metre is the classic setup and it still works, but it puts a lot of heat in. These are bare lamps, so budget a reflector, and we do not stock the fitting.
Where the running-cost difference shows
At this size the comparison stops being about purchase price. An LED fixture of around 300 watts delivers comparable usable light to a 600 watt HPS, at roughly half the consumption and considerably less heat. Count the extraction that heat requires into the difference, because that is where the sum tips.
Compare on stated coverage
Not every product page gives a figure, but at this size most do, and it is the most reliable number to choose on. Where a lamp states a smaller size than your tent, it is not unsuitable but it is aimed at a smaller footprint; you hang it higher and give up intensity.
Frequently asked questions
300 watts of LED or 600 of HPS?
LED if electricity and heat count, HPS if purchase price decides and you can shed the heat. With HPS, count in the reflector and the heavier extraction.
Why do some lamps here state 90x90?
Because they are tuned to a slightly smaller footprint. They work over a square metre, but the light will be weaker at the edges than in the middle.
Do I need metal halide?
Only if you grow on discharge and want a bluer spectrum for the growth phase. With LED the question does not arise.
