Too little light and your plants melt; too much and algae takes the tank. This planted aquarium lighting calculator gives a target light output in lumens for your volume and plant type, plus an LED wattage guide and a photoperiod.
Planted Aquarium Lighting Calculator
Enter your tank volume and how demanding your plants are to get a target light output in lumens, an LED wattage guide, and a photoperiod.
Lumens measure how much light a fixture puts out, which is a better guide than the old watts-per-gallon rule for LEDs. These are starting targets; deep tanks (over 18 inches) need the higher end because light fades with depth. Run the light on a timer for a consistent photoperiod.
Why lumens beat watts per gallon
The old watts-per-gallon rule was built for fluorescent tubes and means little for modern LEDs, which produce far more light per watt. Lumens measure the light a fixture actually puts out, so they carry across fixture types. Deep tanks over 18 inches need the higher end of the range because light fades fast with water depth.
Match the light to the plants
Low-light plants like Anubias, Java fern and mosses thrive on a modest fixture and a 6 to 8 hour day. Our low-maintenance plant guide lists species that grow under a basic LED. Push into high light and you commit to pressurized CO2 and regular dosing, or the surplus light feeds algae instead.
Light is half of the algae equation
Most algae outbreaks are a lighting problem: too many hours, or a tank in direct sun. A plug-in timer holding a steady photoperiod is the cheapest fix in the hobby, covered in getting rid of algae without chemicals. Size the tank first with the aquarium volume calculator, and find the rest on the aquarium calculators hub.
Frequently asked questions
How many lumens does a planted tank need?
Roughly 10 to 20 lumens per liter for low-light plants, 20 to 40 for medium, and 40 or more for high-light carpets. Enter your volume above for the exact range.
How long should I run aquarium lights?
6 to 8 hours a day on a timer. Longer periods feed algae without helping plants.
Do I need CO2 for a planted tank?
Only for high light. Low and medium light tanks grow well without it.