Calculate the right aquarium light wattage by tank type. Fish-only: 1-2 W/gal, planted: 2-5 W/gal, reef: PAR-based lighting.
Aquarium lighting serves both aesthetic and biological purposes. In fish-only tanks, lighting primarily enhances color and viewing pleasure. In planted tanks, lights drive photosynthesis, directly affecting plant growth and health. Reef tanks require specific light spectrums and intensities measured in PAR (photosynthetically active radiation) to sustain corals.
The classic watts-per-gallon rule provides a simple starting point: fish-only setups need 1-2 W/gal, low-tech planted tanks need 2-3 W/gal, and high-tech planted tanks need 3-5 W/gal. However, modern LED fixtures are far more efficient than older fluorescent and metal halide systems, so actual wattage requirements have decreased while light output has improved.
This calculator estimates the recommended wattage range based on your tank volume and setup type, giving you a baseline for choosing the right fixture.
Responsible pet owners, breeders, and veterinary professionals benefit from accurate aquarium lighting data when making care decisions, budgeting for expenses, or monitoring health benchmarks. Revisit this tool whenever your pet's needs, weight, or age changes to keep recommendations current.
Incorrect lighting leads to algae blooms (too much light), poor plant growth (too little), or coral bleaching (wrong spectrum). This calculator helps you select appropriate wattage for your specific tank type, preventing common lighting mistakes that frustrate beginners and experienced hobbyists alike. Instant recalculation lets you explore different options and scenarios, ensuring your pet-care decisions are guided by accurate, reliable numbers.
Wattage = Tank Gallons × Watts-per-Gallon Fish-Only: 1-2 W/gal Low-Tech Planted: 2-3 W/gal High-Tech Planted: 3-5 W/gal Reef: PAR 50-150+ (varies by coral)
Result: 60-90 watts
For a 30-gallon low-tech planted tank at 2-3 W/gal: low end = 30 × 2 = 60W, high end = 30 × 3 = 90W. A 70-80W LED fixture would be a good choice. Modern LEDs may achieve adequate PAR at even lower wattage.
The watts-per-gallon rule was developed when fluorescent lighting was standard. Today's LEDs can produce the same or greater light output at 40-60% less wattage. When shopping for LED fixtures, look at lumens and PAR values rather than watts alone. A 40W LED may outperform an 80W fluorescent tube.
Planted aquariums require a balance of light, CO2, and nutrients. High light without adequate CO2 fertilization leads to algae explosions. Start with moderate lighting and increase gradually while monitoring plant health and algae levels. The "balance of light and nutrients" principle is key to success.
Corals require specific light spectrums to photosynthesize through their symbiotic zooxanthellae. SPS corals need PAR values of 200-400+, while LPS corals thrive at 100-200 PAR. Soft corals and mushrooms are the most forgiving at 50-150 PAR. Always use a PAR meter to verify light levels at coral placement depth.
It is a rough guideline but less accurate for LEDs. LEDs produce significantly more light per watt than fluorescents. PAR measurements are more accurate for planted and reef tanks. Use W/gal as a starting point and adjust based on plant or coral response.
Most tanks do well with 6-8 hours of light per day. Planted tanks may benefit from up to 10 hours with CO2 injection. Longer photoperiods without adequate CO2 and nutrients lead to algae problems.
PAR stands for Photosynthetically Active Radiation, measured in micromoles per square meter per second. It quantifies the light useful for photosynthesis. Low-light plants need PAR 15-30, medium 30-50, and high-light plants 50-100+.
No. Fish need a dark period to rest, just like humans. A consistent 6-8 hour light and 16-18 hour dark cycle mimics natural conditions. Blue moonlight LEDs at very low intensity can be used for nighttime viewing without stressing fish.
Excessive light duration or intensity doesn't directly harm most fish but promotes aggressive algae growth that degrades water quality. Some fish prefer dimmer conditions. Use floating plants to create shaded areas for light-sensitive species.
Freshwater planted tanks thrive at 6500K (daylight). Saltwater reef tanks use bluer spectrums around 10,000K-20,000K to mimic deep ocean light. Fish-only tanks can use any color temperature that looks pleasing.