How to Choose an LED Light for a Planted Aquarium

In a planted aquarium, light drives everything. It feeds your plants, brings out the colours of your fish and gives the whole layout its depth. Get it wrong, though, and you can end up with algae everywhere or plants that slowly fade away. Here is what to check before buying an LED light for a planted tank.

Why lighting makes or breaks a planted tank

Aquatic plants use light to make their own energy through photosynthesis. Without enough of it, they grow tall and spindly, drop their lower leaves and leave the field open to algae. Too much light, unbalanced by nutrients, causes algae as well. So the goal is not to blast the tank with as much light as possible, but to get the balance right.

Measure your tank first

The light should match the length of your aquarium. Too short and the ends of the tank sit in shadow; too long and it simply will not sit on the glass.

• Measure the outside length of the tank, edge to edge.
• Check the glass thickness: the brackets need to grip it securely.
• Go for a light with extendable brackets, so it can follow you if you upgrade your tank later.

Our planted aquarium LED light is a good example: its brackets fit tanks from 30 to 45 cm, with glass up to 10 mm thick.

Spectrum: the real secret of a planted tank

A plain white light does the job, but it can leave plants looking a little flat. A full-spectrum light mixes white LEDs with red and blue ones:

• White gives a natural, bright look.
• Red makes red plants pop and warms up fish colours.
• Blue adds depth and that crystal-clear water effect.

For an aquascape, look for a light described as full spectrum or designed for plants. That is the difference between a basic lamp and proper planted tank lighting.

Power and intensity: finding the sweet spot

Wattage gives you a rough idea, but how much light reaches the bottom also depends on water depth. The taller the tank, the more intensity is lost on the way down. For a 20 to 30 litre nano tank, a light of around 10 to 15 W is plenty for easy plants such as Anubias, Java moss, Cryptocoryne and ferns.

If you are starting out without CO2 injection, stick to moderate intensity. Demanding plants, like carpeting species, need more light and a fair bit more technique.

A timer is your best defence against algae

Algae thrive on inconsistency: 12 hours of light one day, 5 the next. A built-in timer solves that once and for all.

• In a new tank, start with 6 hours of light a day.
• After a month, if plants are growing well and there is no sign of algae, move up to 7 or 8 hours.
• Do not go beyond 8 or 9 hours: past that point plants stop benefiting, but algae keep going.

Ideally, schedule the light for when you are home, such as the evening, so you get to enjoy the tank at its best.

Installation details that matter

A few simple precautions will extend the life of your light:

1. Keep the power supply well away from splashes.
2. Leave a drip loop in the cable so water cannot run down to the socket.
3. Dust the light with a dry cloth, never with household cleaners.
4. On an open-top tank, keep an eye on evaporation and condensation on the diffuser.

Our advice for a 20 litre nano tank

For a first planted tank, the built-in lighting of our 20 L nano aquarium kit is already enough to grow easy plants. If you want to go further, with more colourful species or a carpet, add a full-spectrum light with a timer. The winning combination: a stable tank, a consistent light schedule and a little patience during the first few weeks.

To sum up, a good LED light for a planted aquarium has the right length, a full spectrum, an intensity suited to your water depth and a timer. Tick those four boxes and you give yourself every chance of a lush, bright underwater landscape.