Saltwater Lighting at a Glance
Matching light intensity to coral needs is the key to a thriving reef aquarium.
Coral Light Requirements (PAR)
Light Type
| Light Type | Best For | PAR Output | Pros |
|---|---|---|---|
| LED | All reef setups — most popular option | Up to 400+ PAR | Programmable, energy efficient, long life, full spectrum |
| T5 HO | SPS-dominated tanks, frag tanks | 200-350 PAR | Excellent spread, no disco effect, bulbs cheap |
| Metal Halide | Deep tanks, SPS-heavy systems | 300-500+ PAR | Highest PAR peneration, natural shimmer |
Lighting Schedule: 8-Hour Photoperiod
Reef Lighting Essentials
| Use a PAR meter to measure intensity at different tank depths | |
| Acclimate new corals over 7-14 days (start at 50% intensity) | |
| Maintain consistent photoperiod — timer is essential | |
| Replace LEDs every 3-5 years (spectrum shifts even if still bright) | |
| Account for light falloff: 50% reduction every 6 inches of water depth | |
| Put corals in 'random' spots without checking PAR requirements | |
| Run lights 14+ hours for 'more coral growth' (causes algae blooms) | |
| Skip acclimation — corals 'toughen up' on their own |
PAR (Photosynthetically Active Radiation) is the only reliable way to measure light intensity for corals. A PAR meter costs $150-200 or can be rented from reef clubs. Place the coral where PAR matches its needs — low (50-100), medium (100-200), or high (200-350+). Guessing leads to slow death or bleaching.
The 'disco ball' effect — swirling colors on tank surfaces — happens when cheap LED fixtures don't blend properly. Quality LEDs with diffusers or T5 HO fixtures eliminate this. Your corals don't care about disco, but your viewing enjoyment does.
Reef aquarium lighting must deliver the right spectrum (420-480nm blue/violet for zooxanthellae photosynthesis, with supplemental white) and intensity (PAR -- photosynthetically active radiation -- of 50-75 for low-light soft corals, 100-200 for LPS, 200-400+ for SPS at depth) to sustain coral health. LED fixtures have largely replaced T5 and metal halide systems, offering programmable spectrum and intensity with lower heat output and energy consumption.
| Coral Type | PAR Target | Notes |
|---|---|---|
| Soft corals (mushrooms, zoanthids) | 50–150 umol/m2/s | Lowest demand; excellent starting corals for new reef tanks |
| LPS (hammer, torch, brain, frogspawn) | 100–250 umol/m2/s | Place mid-tank; acclimate from lower end of range |
| SPS (Acropora, Montipora, Stylophora) | 200–500+ umol/m2/s | High demand; acclimate over 4–6 weeks; bleaching if too fast |
Why reef lighting is different from freshwater
Freshwater plant lighting needs photons in the PAR range -- roughly the right quantity, roughly the right spectrum, and plants adapt. Corals are different. The zooxanthellae living inside coral tissue are optimized for the light that filters through tropical seawater to 15-30 feet depth -- a shifted spectrum heavy in blue and violet (short wavelengths that penetrate water better than red), with intensity that varies by depth and position. Put a shallow-water SPS coral under insufficient light and it bleaches in a different direction than one receiving too much light -- and both bleaching events look identical to the untrained eye. Matching light to the specific coral, its depth in the tank, and its position under the fixture is a precision exercise.
Understanding PAR
PAR (photosynthetically active radiation) measures photon flux in the 400-700nm wavelength range in units of micromoles per square meter per second (umol/m2/s). A PAR meter is the essential tool for verifying what your coral actually receives, not what the manufacturer claims. The same fixture produces different PAR at different depths and positions in the tank. General targets: zoanthids, mushrooms, most soft corals: 50-150 PAR; LPS corals (hammer, frogspawn, torch, brain corals): 100-250 PAR; SPS (Acropora, Montipora, Stylophora): 200-500 PAR depending on acclimatization history. These are starting points -- observe coral response over 4-6 weeks after placement.
Spectrum and color temperature
Zooxanthellae peak absorption is around 420-450nm (violet/blue) and 670-680nm (red). In the ocean, red wavelengths are absorbed in the first few feet of water; blue and violet dominate at depth where corals grow. Reef LED fixtures typically blend: deep blue (450nm), royal blue (460-470nm), blue/white, and supplemental white LEDs. The 'blues' drive photosynthesis; white channels produce visual brightness that makes corals appear colorful to human eyes. A fixture running only white light looks bright but under-delivers the blue spectrum corals actually use. The balance varies: FOWLR (fish only with live rock) tanks can run any white-dominant spectrum; mixed reef tanks need significant blue; SPS-dominant tanks may run 70-80% blue during the photoperiod peak.
LED fixture categories
Entry-level: NICREW, Kessil A80, Current USA Orbit Marine -- adequate for FOWLR and soft coral tanks, limited programmability. Mid-range: AI Hydra 32/64, Kessil A360, Radion XR15/XR30 (used), Orphek OR3 bars -- full spectrum programmable, adequate for mixed reef to SPS. High-end: Radion XR30 G5/G6, EcoTech Marine, GHL Mitras -- full programmability, advanced spectrum control, manufacturer PAR data available. DIY/strip options: Maxspect Razor strips, Kessil bars. T5 hybrid rigs (T5 for baseline, LED for color/intensity supplementation) remain popular in competitive SPS systems for their uniform light spread.
Photoperiod and light acclimation
New corals placed under full reef lighting can bleach from light shock. Standard acclimation: reduce intensity to 30-40% for weeks 1-2, increase gradually to target over 4-6 weeks. Signs of light stress: bleaching (loss of color from expelling zooxanthellae) indicates excess light or heat stress; browning (increased zooxanthellae density) indicates insufficient light. Both are recoverable if caught early. Photoperiod: 10-12 hours total, with a ramping schedule (gradual increase from dawn to peak, decrease to dusk) more closely mimicking natural conditions than abrupt on/off cycles. Refugium lighting running on reverse photoperiod (on when display lights are off) stabilizes pH by maintaining nighttime algae photosynthesis.
Coral PAR requirements and zooxanthellae photobiology from Falkowski, P.G. et al. (1990), Science. LED spectrum effects on coral growth from Wijgerde, T. et al. (2012), PLOS ONE. Practical husbandry parameters from Advanced Aquarist and Reef2Reef community-validated guidelines.