Aquarium Lighting Calculator
Estimate lighting needs for low, medium or high-tech planted tanks.
How it works
Modern planting uses PAR rather than watts. As a guide: low-light plants need ~15-30 PAR, medium 30-50 PAR, high-light/carpets 50+ PAR at substrate. Photoperiod of 6-8 hours suits most tanks; longer periods invite algae.
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Formula & Method
Modern planting uses PAR rather than watts. As a guide: low-light plants need ~15-30 PAR, medium 30-50 PAR, high-light/carpets 50+ PAR at substrate. Photoperiod of 6-8 hours suits most tanks; longer periods invite algae.
Example Calculation
For a 45 cm deep tank growing a carpet, you'll want a quality LED delivering ~50+ PAR at substrate, run 7 hours daily, ideally with CO2.
Frequently Asked Questions
How much light do aquarium plants need?
Low-light plants like anubias and java fern need roughly 15-30 PAR at the substrate, medium-light plants 30-50 PAR, and high-light carpeting plants 50-80 PAR or more. Tank depth matters as much as fixture output, since intensity falls with the square of distance.
How long should aquarium lights be on?
Six to eight hours for most planted tanks. Longer photoperiods favour algae without meaningfully increasing plant growth. Start at six hours and extend gradually only if plants show they can use it.
Does watts per litre still work for LED lighting?
No. LED efficiency varies too much between fixtures for wattage to indicate output. Use lumens or, better, the manufacturer's PAR figures at your tank's depth.
Why am I getting algae with a new light?
Almost always because light has increased without a matching increase in CO2 and nutrients. Plants cannot use the extra light, so algae does. Reduce the photoperiod or raise the fixture before adding anything else.