Calculator
Reef PAR Calculator
A fixture's "PAR rating" is one number at one height — usually measured closer to the water than you'll ever mount it. Tell us your real mount height and what you're keeping, and we'll show the PAR each fixture actually delivers at your coral's depth — and whether it lands in your target band. Only the 4 fixtures with published PAR data appear here; we don't guess the rest.
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How this works
PAR (photosynthetically active radiation, measured as PPFD in μmol/m²/s) is the light corals actually use. It falls off with distance — through the air gap to the water, then through the water to the coral. We add your mount height and coral depth into one distance, then read each fixture's PAR at that point from its published curve. Fixtures with a multi-point curve interpolate honestly; single-point fixtures (one manufacturer number) are held flat and flagged — we won't invent a falloff rate we can't cite.
The target bands
Softies and LPS want roughly 75–250 PAR; a mixed reef, 150–300; SPS-dominant tanks, 250–350+. These are community-and-BRS consensus ranges, not hard walls — acclimation matters more than hitting a number exactly. Too much PAR bleaches; too little starves. The goal is landing in the band at the depth your corals sit, then dialing intensity from there.
Why only 4 fixtures?
Because only 4 of the popular fixtures we track publish real PAR data — a manufacturer chart or an independent lab test. The other 7 sell hard on watts and spectrum but never put a PPFD number on paper. We won't rank a light on a number that doesn't exist. The full transparency scorecard, including who publishes what, is in the lighting review. Data updated 2026-07-01.
Sized your light? Size the rest.
Flow and light are the two levers that make or break coral color. Once your PAR is in band, get your turnover right with the flow calculator, and if you're speccing a whole build, the cost calculator itemizes it.
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