Free tool
Reef Light Planner
More reef lighting money is wasted on coverage mistakes than on bad fixtures. Tell us your tank dimensions and what you want to grow, and we will tell you how many fixtures the footprint actually needs, what coverage class to shop, and where depth changes the answer.
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Reference
Fixture count by tank length
LED pucks light a roughly square footprint, and PAR falls off fast outside it. The honest rule: one nano puck per 16 inches, or one full-size puck per 24 inches of tank length. This table works without any of the controls above.
| Tank length | Fixtures needed | Why |
|---|---|---|
| Nano, up to 20 in long | One nano puck (16 by 16 in class) | A 55-watt nano fixture like the AI Prime class covers a 16 by 16 inch footprint, which matches pico and nano tanks from 5 to 25 gallons. |
| Standard 24 to 36 in | One full-size puck (24 by 24 in class) | Full-size fixtures in the Radion XR15 and Hydra 32HD class hold useful PAR across roughly 24 by 24 inches. A 36-inch tank works if corals stay near the center. |
| 48 in and longer | Two or more pucks, one per 24 in | A single fixture over a 4-foot tank leaves a PAR valley at each end. Space one puck over the center of each 24-inch segment. |
How it works
How this tool works
LED reef fixtures have a real coverage footprint that is smaller than the box suggests, and light intensity falls quickly at the edges and with depth. The planner takes your tank length and front-to-back width and divides them by realistic coverage figures for each fixture class, which is how it arrives at a count. Coral goal then sets the intensity class: soft corals thrive under modest PAR, LPS and mixed reefs want more, and SPS and Acropora want the most, mounted higher to spread it.
The result names how many fixtures the footprint actually needs, what coverage class to shop, where depth changes the answer, and which lighting picks on the site fit that class. It does not assume you will buy the most expensive fixture; a pair of mid-range units often covers a long tank better than one flagship.
Reading the result
How to read your result
The fixture count is the line most people get wrong, so trust it before the class. A single fixture over a four-foot tank leaves the ends dim no matter how powerful it is, and corals at the edges tell you within a month.
The class tells you the intensity and spread to shop for, and the depth note tells you whether your tank needs the higher end of that class. If your tank is deeper than about 24 inches, read that note twice; deep tanks are where lighting budgets go wrong.
FAQ
Questions people ask
How many LED fixtures does a 48 inch tank need?+
Usually two, sometimes three for SPS on a wide tank. One large fixture can light the middle, but the ends fall off sharply, which is exactly what the planner accounts for.
What PAR do corals need?+
Soft corals do well around 50 to 150, LPS around 100 to 250, and SPS 250 to 450 or more at the coral. The planner's classes map to those ranges at typical mounting heights.
Does mounting height change the plan?+
Yes. Higher mounting spreads the light and evens out coverage at the cost of intensity, which is why deeper or SPS tanks are told to shop the top of the class. Lower mounting boosts intensity but creates hot spots and shadows.
Can I mix fixture brands?+
You can, but matching spectra and controllers makes the tank look consistent and lets one schedule run everything. Mixing works best when the fixtures are the same class.