For a planted aquarium, use a full-spectrum or WRGB LED light sized to your tank, run it 7–8 hours a day, and match the intensity to your plants, low-light plants need a modest LED, while carpets and red plants need a high-output light plus CO2. Light is the engine of a planted tank: it is what plants convert into growth. Too little and plants melt or grow leggy; too much without CO2 and nutrients to match, and algae takes over. This guide explains exactly how to choose and run lighting for a planted tank in India, light levels, spectrum, hours, the light-CO2-nutrient balance, and how to size it.
Get the lighting right and a planted tank becomes far easier; get it wrong and you spend your time fighting algae and replacing dying plants. Here is how to get it right.
Why light is the most important factor in a planted tank
Plants build tissue through photosynthesis, and light is the energy source that drives it. In a fish-only tank, light is just for viewing; in a planted tank, light is effectively food. This is why a planted tank cannot run on a dim fish-only light, the plants simply starve. But light also has to be balanced with CO2 and nutrients: plants can only use as much light as their CO2 and fertiliser supply allows. Push light beyond that balance and the surplus feeds algae instead. Lighting, CO2 and ferts are the three legs of the planted-tank stool.
How much light do your plants need? (PAR and intensity by plant type)
Light intensity for plants is measured in PAR (µmol/m²/s at the substrate). Most hobbyists in India will not own a PAR meter, so the table also gives a practical lumens-per-litre rule of thumb you can check against any light's box:
| Plant type | Light level | PAR at substrate | Rule of thumb | Examples |
|---|---|---|---|---|
| Low-light (easy) | Low to medium | 15–30 µmol | ~15–25 lumens per litre | Java fern, Anubias, Cryptocoryne, Java moss |
| Medium-light | Medium | 30–50 µmol | ~25–40 lumens per litre | Amazon sword, Vallisneria, many stem plants |
| High-light (demanding) | High + CO2 | 50–80+ µmol | ~40–60+ lumens per litre | Carpeting plants, red plants, dwarf hairgrass |
Beginners should start with low-light plants and a modest full-spectrum LED, they are forgiving, need no CO2, and still look lush. Only step up to high-output lighting when you are ready to add CO2 and regular dosing to match. Remember that depth eats PAR: a light that delivers 50 µmol at 30 cm may deliver only half that at 45 cm, which is why deep tanks need stronger units.
Best spectrum for a planted tank
Plants mainly use light in the red and blue parts of the spectrum, but a balanced white light that includes the full range gives both healthy growth and a natural look. The useful numbers: chlorophyll absorbs most strongly around 430–450 nm (blue) and 640–680 nm (red), and a colour temperature of 6500–7500 K gives the natural daylight look that suits planted tanks best. Your two best options:
- Full-spectrum white LED (6500–7500 K) - a balanced, plant-friendly white. The reliable, good-value choice for most planted tanks.
- WRGB LED - white plus individual red, green and blue diodes. The dedicated red diodes (620–660 nm) drive stronger growth and make red plants and greens far more vivid; the premium choice for show planted tanks.
Avoid lights heavy on blue alone (sold for marine or effect) for a planted display, they can look unnatural and tend to favour algae. For the full comparison, see WRGB vs RGB vs full spectrum.
How many hours for a planted tank?
Run a planted tank for 7–8 hours a day for low-tech setups, and up to 8–10 hours for high-tech tanks with CO2. Start at the lower end, especially in a new tank, and increase only if plants need it and algae stays away. Always use a timer for a consistent photoperiod, and never run the light 24/7. Full detail in how many hours should aquarium lights be on.
The light–CO2–nutrient balance
This is the concept that makes or breaks a planted tank. Think of it as three taps that must be opened together:
- Low light, no CO2: easy, stable, low maintenance. Great for beginners with hardy plants.
- High light, with CO2 and dosing: fast, lush, demanding growth. Needs commitment and regular maintenance.
- High light, no CO2 or ferts: the danger zone, plants cannot use the light, so algae does. Avoid this mismatch.
The most common planted-tank failure is buying a powerful light without the CO2 and nutrients to match. If you run a strong light, support it with CO2 and a proper fertiliser routine. If you keep it simple, keep the light modest too.
How to size the light to your tank
The light should span most of the tank’s length for even coverage, and deeper tanks need stronger lights to push usable light down to the substrate, where carpeting plants live. As a rough India-market guide for planted tanks:
| Tank length | Suggested planted light |
|---|---|
| 1–1.5 ft (nano) | Nano full-spectrum clip-on or small panel |
| 2 ft | Full-spectrum 2 ft planted LED |
| 3 ft | High-output full-spectrum or WRGB 3 ft LED |
| 4 ft+ | High-output panel, or twin units for even coverage |
For a deep tank (above ~45 cm), lean toward a higher-output light regardless of length. More on sizing in what size aquarium light do I need.
Avoiding algae in a planted tank
Algae in a planted tank almost always means the balance is off, usually too much light for the available CO2 and nutrients, too long a photoperiod, or stray sunlight. The fixes: start with a moderate light, cap hours at 7–8, keep the tank out of direct sun, and make sure dosing and CO2 (if used) keep pace with the light. Healthy, fast-growing plants are themselves the best algae defence, because they outcompete algae for nutrients. See aquarium light settings to prevent algae.
Putting it together: a simple planted setup
- Easy low-tech tank: hardy plants (Anubias, Java fern, Crypts), a modest full-spectrum LED, 7–8 hours on a timer, no CO2, light dosing.
- Lush high-tech tank: demanding plants, a high-output full-spectrum or WRGB LED, 8–10 hours, pressurised CO2, and a full dosing routine.
- Every planted tank: a timer, a dark night period, and light matched to CO2 and nutrients.
Pair the lighting with a good filter and the right fertiliser dosing and your plants will do the rest.
Frequently asked questions
What light is best for a planted aquarium?
A full-spectrum or WRGB LED sized to your tank. Use a modest LED for low-light plants and a high-output light (with CO2) for demanding plants.
How many watts or how much light do I need for plants?
Match light to your plants rather than a fixed wattage: roughly 15–25 lumens per litre (15–30 PAR) for low-light plants, 25–40 lumens per litre for medium, and 40–60+ lumens per litre (50+ PAR) with CO2 for carpets and red plants.
How many hours should a planted tank light be on?
7–8 hours for low-tech tanks, up to 8–10 hours for high-tech tanks with CO2. Use a timer and never run it 24/7.
What PAR do aquarium plants need?
Around 15–30 µmol at the substrate for low-light plants, 30–50 µmol for medium-light plants, and 50–80+ µmol (with CO2) for carpeting and red plants.
What colour temperature is best for planted tanks?
6500–7500 K. It matches natural daylight, grows plants well, and renders greens and fish colours naturally.
Can aquarium plants grow with LED lights?
Yes. Modern full-spectrum and WRGB LEDs are excellent for growing aquarium plants and are the standard choice today.
Do I need a special light for live plants?
Yes. Live plants need an adequate full-spectrum light to photosynthesise. A dim fish-only light will not keep most plants alive.
Is WRGB or full spectrum better for plants?
Both work well. Full spectrum is great value; WRGB gives stronger growth and more vivid colour rendering for show tanks.
Why are my plants dying even with a light?
Usually the light is too weak, the photoperiod too short, or CO2 and nutrients do not match a strong light. Check the light-CO2-nutrient balance.
Do I need CO2 for a planted tank?
Not for low-light, hardy plants. CO2 is needed only when you run high light and demanding plants for fast, lush growth.
Can I grow a carpet without a strong light?
Generally no. Carpeting plants need high light reaching the substrate (50+ PAR), plus CO2, to grow flat and dense.
Why do I get algae in my planted tank?
Usually too much light for the available CO2 and nutrients, too long a photoperiod, or sunlight. Rebalance light, hours, and dosing.
Is blue light good for planted tanks?
Blue light alone is not ideal for plant growth or a natural look. Use a full-spectrum or WRGB light; reserve blue for a short evening mode.
How close should the light be to the water?
Close enough for good intensity at the substrate without overheating. Deep tanks need a stronger light or a closer mount.
Can I use sunlight to grow my plants?
Direct sunlight causes severe algae and is hard to control. Use a proper aquarium light on a timer instead, and keep the tank out of the sun.
Will a stronger light grow my plants faster?
Only if CO2 and nutrients keep pace. Otherwise the extra light just feeds algae. Increase light and inputs together.
What light should a beginner planted tank use?
A modest full-spectrum LED with hardy low-light plants, 7–8 hours on a timer, no CO2. It is forgiving and still looks lush.
Ready to plant? Read the full aquarium light guide, then the plant fertiliser guide to complete the picture.
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