Walk into any aquarium shop, and the lights are blazing. At home, many tanks run a bulb for 12 or 14 hours because brighter looks better. Fish and plants see it differently. This guide shows how much light your tank really needs, and why more is rarely better.
Why Aquariums Need Light
- Fish: use light to keep a day and night rhythm, to find food, to breed and to show their colours.
- Plants: use light for photosynthesis. No light means no growth.
- You: use light to enjoy the tank.
Too much light feeds algae and stresses fish. Too little leaves plants weak and fish dull.
How Much Light Does Your Tank Need?
|
Tank type |
Light intensity |
Hours per day |
Notes |
|---|---|---|---|
|
Fish only |
Low to medium |
6 to 8 |
A basic LED is enough |
|
Low-tech planted (anubias, java fern) |
Low |
6 to 7 |
No CO2 needed |
|
Medium planted |
Medium |
6 to 8 |
CO2 or liquid carbon helps |
|
High-tech planted |
High |
6 to 8 |
CO2 and fertiliser are essential |
What Your Fish Need From Light
Fish need a proper day and a proper night. A tank lit around the clock stresses fish, disturbs their rest and invites algae. Switch the light off for a full night. Avoid a sudden blast of light in a dark room, which can startle fish, by turning on room lights first or using a dimmable light. A dim moonlight setting is fine for short evening viewing.
What Your Plants Need
Match plants to the light level, not the other way round. Anubias, Java fern and crypts are happy under low light. Stem plants and carpets need much more, along with CO2 and fertiliser. Start with 6 hours and increase only if plants are healthy. Our planted tank lighting guide goes deeper into light levels.
Choosing a Light
- LED is the best choice today: efficient, cool-running and long-lasting.
- Older fluorescent tubes work but run hotter and need replacing sooner.
- Colour: full-spectrum white around 6000 to 7000 K suits both fish and plants.
- Size: choose a light that covers most of the tank length. Tall tanks need a stronger fixture because light fades with depth.
Common Lighting Mistakes
- Running the light for 10 hours or more.
- Placing the tank where direct sunlight hits it.
- Using no timer, so the schedule changes every day.
- Forgetting that power cuts reset basic timers.
- Buying a high-intensity light for low-light plants.
If algae has already appeared, read our guide on how to reduce algae growth.
