Dialing in reef tank lighting is one of the biggest keys to colorful, healthy corals. Between PAR numbers, spectrum charts, and endless fixture options, it’s easy to feel overwhelmed. The good news: once you understand a few lighting basics, you can make confident choices and stop constantly tinkering with your lights.
Understanding Reef Tank Lighting: PAR, Spectrum, and Photoperiod
PAR: How Much Light Do Corals Really Need?
PAR (Photosynthetically Active Radiation) measures the usable light for photosynthesis. Different coral types prefer different PAR ranges:
- Soft corals & mushrooms: ~50–100 PAR
- LPS corals: ~75–150 PAR
- SPS corals: ~200–350 PAR (sometimes higher for advanced systems)
If you don’t own a PAR meter, start with the manufacturer’s recommended mounting height and intensity, then watch your corals closely. Pale, washed-out tissue can indicate too much light; stretching and reaching upward often means too little.
Spectrum: Why Blue Light Dominates Reefs
Most reef keepers run a blue-heavy spectrum because:
- Blue wavelengths (around 420–470 nm) drive coral photosynthesis efficiently.
- They bring out fluorescent pigments, giving corals that glowing, high-contrast look.
- They penetrate water better than red or green light.
White, red, and green channels are still useful for color balance and realism, but avoid cranking them to 100%. Many hobbyists find success with a blue-dominant profile and modest white for a natural, slightly cool appearance. For a deeper dive into dialing in color, see our guide on coral coloration and lighting.
Photoperiod: How Long Should the Lights Be On?
Corals don’t need blazing light from dawn to midnight. A simple schedule works best:
- Ramp up: 1–2 hours of gradual increase.
- Main photoperiod: 6–8 hours of peak intensity.
- Ramp down: 1–2 hours back to low blue “evening” light.
This mimics a natural day and helps reduce stress from sudden on/off transitions.
Choosing and Positioning Your Reef Lights
Types of Reef Lighting
Modern reef tanks mostly use three categories of lighting:
- LED: Energy-efficient, controllable spectrum, and compact. Great for most tanks and very popular.
- T5 fluorescent: Excellent spread and proven coral growth, though less control and bulb replacement is required.
- Hybrid (LED + T5): Combines LED shimmer and control with T5 coverage, ideal for larger or SPS-heavy systems.
For help matching light types to your tank size and coral mix, check our overview of reef tank equipment basics.
Height, Spread, and Avoiding Hot Spots
Mounting height and spacing matter as much as overall power. A few quick guidelines:
- Mount height: 8–12 inches above the water is a common sweet spot for LEDs.
- Overlap beams: On longer tanks, use multiple fixtures with overlapping light cones for even coverage.
- Rockwork placement: Put high-light corals toward the top and lower-light species toward the bottom or shaded areas.
Whenever you change height or intensity, do it slowly over 1–2 weeks so corals can adapt.
Practical Tips for Stable, Coral-Safe Lighting
- Use acclimation modes: Many LED units include an acclimation program—use it when upgrading lights or increasing intensity.
- Avoid chasing numbers daily: Set a reasonable schedule, then give corals several weeks before making big changes.
- Clean lenses and splash guards: Salt creep and dust can noticeably reduce PAR over time.
- Pair lighting with nutrients: Intense light plus ultra-low nutrients can cause pale or burnt corals. Balance lighting with feeding and filtration.
- Document your settings: Take screenshots or notes of your light schedule so you can track what works.
Reef lighting doesn’t have to be mysterious. By understanding PAR, spectrum, and photoperiod—and by choosing fixtures that fit your tank’s size and coral mix—you can create a stable, predictable environment where corals thrive. For your next step, check out our guide on beginner reef tank setup to tie your lighting plan into filtration, flow, and stocking choices.
Sources: Bulk Reef Supply Investigates lighting series; Dana Riddle’s articles on coral photobiology; manufacturer documentation from major reef lighting brands (Ecotech, AI, Kessil).
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