Planted Tank LED Light Guide

How high-output planted-tank LEDs drive photosynthesis, how to balance light with CO2 and nutrients, and how to set intensity and photoperiod to avoid algae.

What it is

A planted tank LED is a high-output fixture aimed at planted and aquascaped aquariums, including demanding species. Light provides the energy plants use for photosynthesis, so a stronger fixture supports faster and denser growth than a basic community light. Many planted-tank LEDs offer adjustable intensity and a controllable spectrum.

How it works

Plants use light as one of three key inputs, alongside nutrients and carbon dioxide. A high-output LED supplies the higher light levels demanding plants need, but light must be balanced with the other two inputs. Adjustable intensity and a controllable spectrum let the fixture be tuned to the plant mass rather than run flat out. If intensity exceeds what the plants can actually use, the surplus light and nutrients favor algae rather than growth, which is why too much light is a common cause of algae in planted layouts.

Light, CO2 and nutrients

Because plants and algae share the same resources of light, nutrients, and carbon dioxide, the goal is to balance the three so plants grow strongly and outcompete algae. Demanding plants such as dwarf hairgrass and dwarf baby tears generally require supplemental CO2 for the best results, while easier plants do not. Raising light without matching CO2 and fertilization commonly triggers algae.

Choosing and sizing

A planted fixture is selected for its intensity and spectrum as well as tank length, broadly serving aquascaped tanks from about 30 to 200 litres. A dimmable unit is valuable because a light at full brightness may be too strong; starting around 20 to 40 percent and adjusting upward lets the same fixture grow both low- and high-light plants.

Photoperiod

A common starting photoperiod is 6 to 8 hours per day, extendable toward 8 to 12 hours, ideally run on a timer for consistency. The light should not stay on all night, since plants need a dark period for respiration. Where CO2 is injected, it is timed to the photoperiod.

Maintenance

The fixture is long-lived; upkeep is mainly keeping the lens clean so output stays consistent, and reviewing intensity and photoperiod as the plant mass changes. A typical review interval is roughly once a year.