What matters in a planted-tank light
The biggest beginner lighting mistake is thinking “more is better.” It’s not. Planted tank lighting is about matching intensity and duration to your plant selection and nutrient supply. A high-tech light on a low-tech tank grows algae; a low-tech light on a high-tech tank stunts plants.
Three tiers, three philosophies:
Low-tech (no CO₂): Budget LEDs like the Hygger 957. Enough for Anubias, Java fern, Cryptocoryne, Vallisneria, and other undemanding species. Target 20–40 PAR at substrate. 6–8 hours per day. Keep it simple; the plants don’t need more.
Medium-tech (no CO₂ or liquid carbon): Fluval Plant 3.0 or equivalent. Programmable, dimmable, enough PAR (40–55 at substrate) for stem plants and less-demanding carpets. Ramp intensity over sunrise/sunset periods for better plant response and less algae.
High-tech (CO₂-injected): Week Aqua P600 Pro class lights. 60–100+ PAR at substrate. Discrete color channels for accurate spectrum rendering, so reds pop and the tank looks like a magazine photo rather than blue-tinted. Under this tier, carpeting plants don’t carpet, red plants don’t color up, and demanding species stall.
PAR vs lumens vs wattage
These three terms get confused. What they actually mean:
- Lumens. Brightness as perceived by human eyes. A high-lumen light can have mediocre plant output.
- PAR (photosynthetically active radiation). Light in the 400–700 nm range that plants actually use. This is the number that matters for plant growth.
- Wattage. Electrical consumption. LEDs at 30 watts can produce similar PAR to a 50-watt LED from an older design. Wattage isn’t a useful output metric.
When comparing lights, look for PAR values at specific depths (typically “at substrate” on a given tank depth). Manufacturers increasingly publish these; independent reviewers (BRS, Md Fish Tanks, Green Aqua) measure and post them.
Duration and schedule
6–8 hours per day is the target for almost all planted tanks. Less and plants don’t get enough; more feeds algae without feeding plants much more (plants saturate around 6–8 hours).
Start at 6 hours and 50–60% intensity when a tank is new. Algae colonizes before plants establish, and strong light fuels the algae. Gradually increase to 7–8 hours and 70–80% intensity over 4–6 weeks as plants fill in.
Consistent schedule matters. Plants adapt to photoperiod; algae exploits inconsistency. Use a timer or app-controlled schedule. Don’t run lights manually on random schedules.
Siesta period (split photoperiod with a midday off-period) is a hobbyist strategy where lights run 4 hours morning, 3 hours off, 4 hours evening. Some claim it reduces algae; the evidence is mixed. Not necessary, but worth trying if you struggle with specific algae types.
Mounting height
Most LED fixtures are designed to sit on the tank rim. Raising them 2–4 inches above the water surface:
- Spreads light more evenly across the tank
- Reduces hotspots directly under the fixture
- Increases visual appeal (pendant-style looks more sophisticated than rim-mounted)
- Gives you room for emergent plants or floating plants
Suspension kits (hanging from ceiling or wall-mount arms) cost $30–80 and transform the look of a tank.
Common lighting mistakes
- Buying a reef-spectrum LED for a planted tank (too blue; plants want more red)
- Running lights 10–12 hours a day “to feed the plants”
- Placing the light directly on the glass lid (poor coverage, hotspot directly below)
- Turning the dimmer to max without matching CO₂ and ferts
- Using a cheap light that dies in 6 months, then spending more on the replacement than a quality light would have cost