LED Aquarium Lighting: Grow Healthy Plants Without Feeding the Algae
Lighting isn't just for admiring your fish: it drives your plants' photosynthesis. Too weak, and the plants languish; too strong or too long, and the algae explode. LED light units have now replaced fluorescent tubes, and that's excellent news: lower power consumption, a lifespan of 30,000 to 50,000 hours and better-controlled spectrum.
How many lumens for a planted tank?
The simplest benchmark for a freshwater aquarium is the lumens-per-litre ratio:
- 10 to 20 lm/l: low light, sufficient for anubias, Java fern and mosses.
- 20 to 40 lm/l: medium light, suited to the vast majority of beginner planted tanks.
- Over 40 lm/l: high light, reserved for heavily planted tanks with fertilisation and CO2 injection.
For a standard 100-litre tank, a light unit delivering 2,000 to 3,500 lumens is therefore a good starting point. Budget-wise, expect 30 to 80 € for an entry-level LED unit and 100 to 250 € for a powerful model with adjustable spectrum, from manufacturers such as JBL, Eheim or Tetra.
Spectrum: aim for a white around 6,500 K
A colour temperature of 6,500 to 8,000 K reproduces daylight and suits aquarium plants perfectly. Adjustable units let you fine-tune the red and blue channels, which is useful for intensifying the hues of red plants. Avoid novelty lighting that is permanently blue-only or multicoloured: it encourages algae with no benefit to the plants.
Photoperiod: discipline pays off
The right rhythm: 6 to 8 hours a day when starting out, then up to 10 hours once the tank is balanced — always in a single block. A mechanical timer or a smart plug (5 to 15 €) makes the routine automatic and consistent: plants and fish alike appreciate regularity. If algae start gaining ground, shorten the photoperiod before changing any equipment, and check your parameters with good water tests.
Lighting and plant choice go hand in hand
There's no point investing in a high-end light unit for a tank of anubias, nor hoping for a carpet of demanding plants under 15 lm/l. Define your planting project first — the lighting follows. Our comparison of live versus artificial plants will help you decide, and the Planète Pets fishkeeping hub gathers all our equipment guides to build a coherent tank, from the light down to the substrate.
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.