Dialing in reef LED lighting can feel confusing, but it doesn’t have to be. Understanding a few basics about spectrum, intensity, and photoperiod will help you grow healthy corals, show off vivid colors, and avoid nuisance algae. In this guide, we’ll walk through the fundamentals so you can confidently tune your LEDs for your reef tank.
Why Spectrum Matters for Coral Health
Corals host symbiotic zooxanthellae (algae) that rely on light for photosynthesis. Reef LEDs are designed to target the wavelengths these organisms use most efficiently, especially in the blue range.
Key Spectrum Ranges
- Royal blue (around 450–460 nm) – Primary driver of photosynthesis and the classic reef “glow.”
- Blue (around 420–470 nm) – Supports growth and enhances fluorescence in LPS and SPS corals.
- Violet/UV (around 380–420 nm) – Can deepen coloration but should be used moderately.
- White (cool and warm) – Fills in the spectrum for a more natural look and better color rendering of fish and rock.
For most mixed reefs, a blue-heavy spectrum with a modest amount of white produces strong growth and vivid coloration. If you’re just getting started, check out our overview on beginner reef tank setup to make sure your lighting plan matches your livestock goals.
Intensity and PAR: How Bright Is Bright Enough?
LEDs are powerful. Running them at 100% rarely equals better growth and can quickly bleach corals. Instead, aim for target PAR (Photosynthetically Active Radiation) ranges that match your coral types:
- Soft corals & zoas: ~50–150 PAR
- LPS corals: ~75–200 PAR
- SPS corals: ~200–350+ PAR
Tip: When in doubt, start lower and increase intensity slowly over several weeks. Corals handle an increase in light much better than a sudden blast of high PAR.
If you don’t have a PAR meter, you can still tune intensity safely:
- Begin at 30–40% overall power on most LED fixtures.
- Watch for signs of stress: pale tissue or receding color often means too much light.
- Increase intensity by 5–10% every 7–10 days if corals look healthy and expanded.
Mounting height also affects intensity and spread. Many reefers find a sweet spot around 8–12 inches above the water, but this depends on the fixture and tank dimensions. For more on balancing light with nutrient levels, see our guide on nutrient control in reef tanks.
Photoperiod and Daily Light Schedule
Corals don’t need 14+ hours of intense light. In fact, too long a photoperiod can fuel algae and stress certain species. A simple, effective LED schedule looks like this:
- Ramp-up (blue-heavy): 1–2 hours
- Main photoperiod: 6–8 hours at peak intensity
- Ramp-down (blue-only): 1–2 hours
This gives you 9–12 total hours of light with only 6–8 hours at maximum power, mimicking a natural sunrise–midday–sunset pattern while protecting corals from overexposure.
Practical Hobbyist Tips
- Use your LED’s preset “reef” profiles as a starting point, then tweak slowly.
- Resist the urge to constantly change settings; give corals 1–2 weeks to respond.
- Take photos under the same lighting each week to track color and growth changes.
- Combine stable lighting with consistent parameters, as discussed in our reef tank maintenance schedule.
In the end, reef LED lighting basics come down to three things: a blue-focused spectrum, appropriate intensity, and a reasonable photoperiod. Start conservative, adjust gradually, and let your corals “tell” you how they feel. With a bit of patience and observation, your LEDs can deliver both healthy growth and a stunning display you’ll enjoy every time the lights come on.
Sources
- Borneman, E. H. (2001). Aquarium Corals: Selection, Husbandry, and Natural History.
- Delbeek, J. C., & Sprung, J. (1994–2005). The Reef Aquarium Vol. 1–3.
- Riddle, D. (2017). Lighting the Reef Aquarium.
- Dana Riddle, “Photosynthesis and Reef Aquarium Lighting,” various articles and presentations.
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