Planted Tank Lighting: Intensity, Duration and Algae Control (Part 2 of 4)

Mayur Dev|13 अक्तूबर 2026

Light decides how fast your plants grow and how fast algae can follow. Learn the difference between low, medium and high light, how many hours to run your lights, why spectrum matters, and how to stop algae before it starts. Part 2 of our Planted Tank Series.

Light is the accelerator pedal of a planted tank. More light means faster growth, and faster growth means a bigger appetite for nutrients and CO2. Press too hard and algae takes the wheel. In Part 1, we built the foundation. Now we choose how much light to put on it.

Light Levels: Low, Medium and High

Level	Approx. PAR at substrate	Typical plants	What it needs
Low	15 to 30	Anubias, Java fern, cryptocoryne, Java moss	No CO2, light fertilizing
Medium	30 to 50	Many stem plants, swords, vallisneria	CO2 helps, regular fertiliser
High	50 and above	Carpeting plants, demanding red stems	CO2 and full fertilising are essential

PAR is the light plants can actually use. Few hobbyists own a PAR meter, so treat these as approximate and check the manufacturer's guidance for your light and tank depth.

Why Watts per Litre Is Outdated

LED efficiency varies widely, so wattage tells you little. Tank depth matters more than people expect, because light fades as it travels down. A tall tank can receive far less light at the substrate than a shallow one under the same fixture. Use the manufacturer's PAR or coverage data, then watch how your plants respond.

Photoperiod: How Many Hours?

Start with 6 hours a day. Most planted tanks do well at 6 to 8 hours. Increase by 30 minutes at a time, and only if the plants are healthy and free of algae. A common trick is a siesta: lights on for 3 hours, off for 3, then on for 3 again. Always run the light on a timer.

Two India-specific tips:

Power cuts reset cheap timers. Use a timer with battery backup, or check it after any outage.
Keep the tank out of direct sunlight. A window beam can add hours of uncontrolled light and trigger algae growth.

Spectrum: What Colour of Light?

A full-spectrum white light around 6000 to 7000 K is a safe starting point for plants. Red and blue channels can enhance plant and fish colour, but a purely blue or green-heavy light does little for growth.

Light and Algae

Most algae outbreaks in planted tanks are not a lighting problem on their own. They happen when light is stronger than what CO2 and nutrients can support. Fix this by reducing the hours or intensity first, before reaching for any treatment. Floating plants also help by diffusing the light. Our guide on reducing algae growth goes deeper.