Equipment guide
Aquarium Lighting
How much light your plants actually need, and why brighter isn't better.
By Mike Elmira
TL;DR, Aquarium Lighting
Light drives plant growth, but it drives algae just as hard, so the goal is to match light to what your plants and CO2 can keep up with, not to fit the brightest fixture you can find. Low-light plants like anubias, java fern, crypts and mosses want modest light and no CO2. Demanding carpets and red stems want strong light plus CO2, or they melt and hand the extra light to algae instead. Run six to eight hours on a timer and adjust from there.
Light demand by plant type
Rough PAR at the substrate. Pair high light with CO2.
- Low (anubias, java fern, crypts, mosses)
- ~15 to 30 PAR, no CO2 needed
- Medium (most stems, easy carpets)
- ~30 to 50 PAR
- High (demanding carpets, red stems)
- 50+ PAR, CO2 required
- Photoperiod
- 6 to 8 hours on a timer
How much light you need
Plant demand is usually described in PAR, the amount of usable light reaching the substrate. Easy plants are happy in low light, most stems and easy carpets want medium, and demanding carpets and reds need high light and the CO2 to match. If you give high light without CO2 and nutrients to back it, the plants can't use the extra and algae takes it instead. When in doubt, start lower and raise it slowly.
Photoperiod
Six to eight hours a day suits most planted tanks, on a timer so it stays consistent. Longer does not mean more growth, it mostly means more algae. If you get algae, shorten the day before you reach for anything else. A consistent schedule matters more than the exact length.
Depth and spread
Light falls off fast with depth, so a tall tank needs a stronger fixture to reach the same PAR at the substrate as a shallow one. Spread matters too: a single spotlight leaves dark corners where plants sulk and algae settles. Aim for even coverage across the whole footprint.
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
Is too much light bad for a planted tank?
Yes. Light the plants can't use, because they're short on CO2 or nutrients, goes straight to feeding algae. Match light to your plants and CO2, and start lower rather than higher.
How long should aquarium lights be on?
Six to eight hours a day on a timer suits most planted tanks. Longer mostly grows more algae, not more plant. If algae appears, shorten the photoperiod first.