The short answer
The best light for a planted tank is full-spectrum or RGB — it delivers the red and blue wavelengths plants photosynthesise with while rendering fish and foliage in rich, natural colour. A daylight colour temperature around 6500K is the reliable benchmark. In short, aim for a broad spectrum, not a single tint.
Why full-spectrum wins
Plants photosynthesise most strongly in the red and blue parts of the spectrum, so a good planted light needs plenty of both. But a light that’s only red and blue turns the tank an unnatural purple and makes fish look washed out. A full-spectrum or RGB fixture solves both problems at once:
- Covers the red and blue plants crave for strong growth.
- Includes green and white for natural colour rendering.
- Makes reds in plants and fish pop, which pure daylight white can mute.
That’s why RGB and full-spectrum lights have become the default for serious planted tanks — they’re a genuine best-of-both.
Getting it right in practice
If your fixture is tunable, start at a balanced daylight-white with the red and blue channels active, then nudge to taste — a touch more red deepens plant and fish colour. Remember that intensity and photoperiod matter more than colour for actually growing plants; the right spectrum makes a well-lit tank look its best, but it won’t rescue a tank that’s too dim or lit too briefly.
Keep the light on a steady 6–8 hour timer and match its intensity to whether you’re running CO2.
For choosing a fixture see our best light for a planted tank guide and browse aquarium lighting. Related equipment answers: how much light do plants need?, what is PAR? and do LED lights cause algae?