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Reef tank lighting works best when matched to coral type, depth, and measured PAR — blue-heavy LED spectra are the common starting point.
Most reef lighting mistakes start the same way: choosing wattage before knowing the PAR your corals actually need. Skip the wattage marketing and treat this reef tank lighting guide as the shortcut — match PAR to coral type, keep the spectrum blue-heavy, and ramp intensity slowly. Those three calls, made in that order, prevent most of the lighting problems that plague new tanks.
What PAR Level Do Corals Actually Need?
PAR — photosynthetically active radiation — measures how much usable light reaches a coral, and it matters more than wattage or brand. Photosynthesis runs on the 400–700 nm band, so any light outside that range does little for coral growth. Each coral group has a well-documented target bracket.
| Coral Type | Target PAR | Best Placement |
|---|---|---|
| Soft corals (mushrooms, zoanthids, leathers) | 50–150 | Low rockwork and shaded edges |
| LPS (torches, hammers, brains) | 100–250 | Mid-level rockwork |
| SPS (Acropora, Montipora, stylophora) | 200–450+ | Upper rockwork, closest to the light |
| Anemones (bubble-tip, carpet) | 150–250 | Mid-level sand or rock |
| Mixed-reef goal | 150–300 across the aquascape | Zone each coral to its bracket |
Light intensity drops quickly with depth, so a PAR reading taken at the coral’s height beats the wattage on the box. For a mixed reef, the usual starting point is blue-heavy light at moderate intensity, tuned zone by zone. The placement pattern follows the brackets: SPS (small-polyp stony corals) high, LPS (large-polyp stony) mid, soft corals low or tucked under overhangs. When a coral is struggling, moving it down before raising the light gives it the gentler path to adjust.
PAR is defined only over that 400–700 nm window, so a meter reading outside the band says little about photosynthesis. Fixture choice should also account for tank depth — the deeper the tank, the more intensity you need at the bottom.
LED Fixture Sizing for Reef Tank Lighting: Wattage, Spectrum, and Coverage
Fixture size follows tank length plus the corals you plan to keep.
Coverage matters as much as raw output. Even coverage is part of the point: one strong fixture creates a bright hotspot with shaded corners, while several smaller lights even out PAR across the aquascape.
Spectrum is where most fixtures win or lose. Reef corals respond strongly to 420–470 nm blue light — royal blue at 450 nm and actinic at 420 nm are the workhorses for growth and fluorescence — and When you’re ready to buy, our tested aquarium reef LED picks compare top fixtures by output and tank fit instead of marketing watts.
Ramping Up New Reef Lighting Without Bleaching Corals
New lighting should start at 30–40% intensity and climb slowly over about a month. That gradual increase lets corals build protective pigmentation before the light gets strong, and it works whether you’re replacing one fixture or lighting a fresh tank.
The setup order that works:
- Set the photoperiod. Run the lights 8–12 hours total, with 1–2 hour sunrise and