Aquarium Lighting Calculator
Calculate the right light intensity, wattage, and photoperiod for your fish-only, planted, or reef aquarium.
Lighting Schedule
Shallow tank - most LED fixtures will provide adequate PAR at the substrate
PAR Guide by Tank Type
Recommended Lights
How It Works
This calculator estimates your lighting needs based on tank dimensions and purpose. It considers the surface area of your tank (length x width) and the depth, which significantly affects how much light reaches the substrate.
PAR (Photosynthetically Active Radiation) is the gold standard for measuring aquarium light intensity. It measures the number of photons in the 400-700nm range reaching a given area per second. Different organisms have different PAR requirements.
Tank depth matters. Light intensity drops significantly with depth due to absorption and scattering. A light that provides 100 PAR at the surface of a 12-inch tank may only deliver 40 PAR at the substrate of a 24-inch tank. Deeper tanks require proportionally more powerful lights.
Photoperiod (hours of light per day) should be consistent. Use a timer and include a 30-60 minute ramp-up and ramp-down period to simulate natural sunrise and sunset conditions, which reduces stress on fish.
Frequently Asked Questions
What is PAR and why does it matter for aquariums?
PAR (Photosynthetically Active Radiation) measures the light intensity that plants and corals can actually use for photosynthesis, in the 400-700nm wavelength range. Unlike lumens (which measure brightness to the human eye), PAR tells you how much usable light energy reaches your plants or corals. Low-tech plants need 40-80 PAR, high-tech plants need 80-150 PAR, and most corals require 150-300+ PAR at their position in the tank.
How long should I keep my aquarium light on?
Fish-only tanks need 6-8 hours of light per day. Planted tanks do best with 8-10 hours. Reef tanks typically run 10-12 hours. More light time does NOT compensate for insufficient intensity -- if your light is too dim, running it longer will just cause algae. Use a timer for consistency, and consider a gradual ramp-up/ramp-down period to simulate sunrise and sunset, which reduces fish stress.
Why am I getting algae with my aquarium light?
Algae thrives when there is an imbalance between light, nutrients, and CO2. The most common causes are: too many hours of light per day (reduce to 6-8h initially), light that is too intense for a low-tech setup, direct sunlight hitting the tank, or excess nutrients without enough plants to compete with algae. In planted tanks, adding CO2 and more fast-growing plants often solves algae issues better than reducing light.
Do I need a special light for a planted aquarium?
For low-tech plants (java fern, anubias, crypts), a basic full-spectrum LED in the 6500K color temperature range is sufficient. For high-tech planted tanks with carpeting plants and stem plants, you need a dedicated planted tank light with higher PAR output and ideally a full RGB spectrum. Budget options like the Nicrew ClassicLED Plus work well for low-tech, while the Fluval Plant 3.0 is excellent for high-tech setups.