Aquarium light calculator
Estimate the lumens and rough LED wattage your planted tank needs for a low, medium or high light setup.
How the estimate works
Plants are driven by the amount of light that reaches them, which is easier to compare in lumens than in watts. The calculator converts your volume to liters and multiplies by a target rate for your chosen level: about 15 lumens per liter for low light plants, 30 for medium and 50 or more for high light. It then reports the total lumens, the lumens per gallon, and a rough LED wattage using a typical efficiency of around 100 lumens per watt.
Treat the wattage as a guide only, because LED fixtures vary a great deal in how much light they produce per watt. Volume is a simple stand in for tank size here, but light fades quickly with depth, so a tall tank needs more output to push the same light down to the substrate. Where a manufacturer lists PAR at depth, that is an even better number to compare than lumens.
Getting good growth without algae
More light is not automatically better. Bright light speeds up plant demand for carbon dioxide and nutrients, and when those run short the extra light feeds algae instead. Match your light level to your plants and your willingness to dose fertilizers or add carbon dioxide. Low light plants like anubias, java fern and cryptocoryne thrive on modest lighting and little fuss, while carpeting plants and red stems usually need high light plus extra support.
Use a full spectrum light in the daylight range of about 6500 to 7500 Kelvin, run it on a timer for a steady 6 to 8 hours a day, and adjust from there. If you see algae building up, shorten the photoperiod or lower the intensity before adding more light.
Frequently asked questions
How many lumens does a planted aquarium need?
As a guide, low light plants want about 15 lumens per liter, medium light around 30, and high light plants 50 or more. This tool multiplies your volume by the rate for your chosen level.
Is watts per gallon a good way to size a light?
Not anymore. Watts per gallon was built around old fluorescent tubes. Modern LEDs vary widely in efficiency, so lumens and, where available, PAR are far better guides than raw wattage.
What color temperature is best for plants?
A daylight range of about 6500 to 7500 Kelvin looks natural and supports plant growth. Full spectrum lights that include some red and blue tend to give the best results.
How long should the light be on?
Start with a photoperiod of about 6 to 8 hours a day on a timer. Longer periods or very bright light without enough carbon dioxide and nutrients tend to feed algae rather than plants.