Aquarium Lighting Calculator
Calculate the recommended lighting intensity and photoperiod for your aquarium based on tank size and plant or coral requirements.
Aquarium lighting serves multiple purposes: it makes the tank visually beautiful, supports live plant and coral photosynthesis, and regulates the biological rhythms of fish. Choosing the right amount of light is one of the most important factors in aquarium health.
Key lighting metrics:
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PAR (Photosynthetically Active Radiation) — Measures the intensity of light usable for photosynthesis, in µmol/m²/s (micromoles per square meter per second). PAR is the most accurate metric for planted tanks and reef tanks.
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Lumens per gallon (LPG) — An older approximation still useful for basic freshwater tanks. Roughly:
- Low light plants: 10–20 LPG
- Medium light plants: 20–40 LPG
- High light plants: 40–80+ LPG
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Watts per gallon (WPG) — Outdated metric (designed for fluorescent tubes, not LEDs), but still widely referenced in older aquarium guides.
Recommended PAR levels by tank type:
| Tank Type | PAR (µmol/m²/s) | Hours/Day |
|---|---|---|
| Fish-only (no plants) | 20–50 | 8–10 |
| Low-light planted (Java fern, Anubias) | 20–50 | 8–10 |
| Medium-light planted | 50–150 | 8–10 |
| High-light planted / Dutch style | 150–400 | 6–8 |
| Soft coral / LPS reef | 50–150 | 10–12 |
| Mixed reef | 150–300 | 10–12 |
| SPS (small polyp stony) reef | 250–450+ | 10–12 |
Photoperiod — why it matters: Running lights too long (14+ hours/day) causes algae outbreaks because algae can photosynthesize at lower light levels than most aquatic plants. Keep lights on for 8–10 hours for planted tanks and use a timer.
Metric and imperial:
- Tank volume in liters or gallons can be used (1 US gallon = 3.785 L)
- Tank dimensions in cm or inches both work for footprint-based calculations
LED efficiency note: Modern LED fixtures produce dramatically more PAR per watt than older T5 or T8 fluorescent tubes. The “watts per gallon” rule was designed for fluorescent lighting and significantly overestimates how much LED power you need. Always use PAR values when sizing LED fixtures.