Aquarium Lighting for Reef Tanks: Coral PAR & Spectrum Needs

Aquarium Lighting for Reef Tanks: Coral PAR & Spectrum Needs | Aqualista

🪸 Grow vibrant, healthy corals — This guide covers PAR requirements for SPS, LPS, and soft corals, spectrum science, acclimation, and reef lighting strategies backed by research.

What PAR Do SPS, LPS, and Soft Corals Need?

SPS corals require 200–350 PAR (Acropora up to 500), LPS prefer 75–150 PAR, and soft corals thrive at 50–100 PAR. Zoanthids tolerate up to 200 PAR.

PAR directly influences coral growth, coloration, and health. SPS (Small Polyp Stony) corals like Acropora demand high light because their zooxanthellae need intense energy to calcify. LPS (Large Polyp Stony) corals, such as Euphyllia, are more moderate. Soft corals (e.g., Sinularia) adapt to lower light. Reefs.com research shows that Acropora grows 3x faster at 350 PAR vs 150 PAR. Always measure PAR at the coral’s actual location (not just water surface), using a quantum meter. Place high‑light species on top of rockwork, low‑light species on the sand bed or shaded overhangs.

🪸 SPS corals
Acropora, Montipora, Pocillopora
200–350 PAR (Acro up to 500)

🐚 LPS corals
Torch, Hammer, Duncan, Acanthophyllia
75–150 PAR

🌊 Soft corals
Zoanthids, Mushrooms, Leathers
50–100 PAR (zoas up to 200)

Why Does Blue Spectrum Dominate Reef Aquarium Lighting?

Blue light (420–470 nm) penetrates water deepest, matches zooxanthellae absorption peaks, and triggers coral fluorescence. Most reef LEDs run 70–80% blue/violet channels.

In the ocean, red light is absorbed within the first 5 meters, while blue reaches depths beyond 30 meters. Zooxanthellae algae evolved to use blue wavelengths most efficiently. Blue light also stimulates green fluorescent protein (GFP) and other photoprotective pigments, giving corals their brilliant colors. NOAA Coral Reef Watch confirms that shallow Acropora receives about 30% blue light, while deeper corals see almost only blue. Therefore, reef lights dedicate 60–80% of their LEDs to blue/violet (400–480 nm). A popular schedule: 100% royal blue + 80% blue + 20% white for peak hours, then moonlights overnight.

💡 Pro tip: Run an “actinic only” period (420nm) for the first and last hour of the photoperiod – this makes corals fluoresce beautifully and simulates dawn/dusk.

How to Acclimate Corals to New LED Lighting Without Bleaching?

Start PAR at 50% of target for 1–2 weeks. Increase by 10% weekly over 4–6 weeks. Watch for tissue swelling or retraction as stress signs.

Corals need gradual adaptation to higher PAR. A sudden increase of 100 PAR can cause photoinhibition and bleaching. Use your light’s acclimation mode or manually reduce intensity. Bulk Reef Supply recommends a 6‑week schedule: week 1‑2 at 50%, week 3 at 65%, week 4 at 75%, week 5 at 85%, week 6 at 100%. Observe corals daily: slight tissue expansion is good; retraction or paling means slow down. For SPS, brown‑out (zooxanthellae increase) indicates too little light. Fluorescent protein enhancement appears when light is adequate.

🚨 Bleaching warning: If you see white skeleton through translucent tissue, reduce PAR immediately by 30% and shorten photoperiod to 6 hours for 2 weeks.

How to Measure PAR in a Reef Tank?

Use a quantum meter with an underwater cosine‑corrected sensor (Apogee MQ‑510 or Li‑COR LI‑192SA). Measure at the exact spots where corals sit, during peak photoperiod.

Place the sensor at coral level, pointing upward. Take 3–5 readings per location and average them. For SPS on rockwork, measure both top and sides of the rock. Create a PAR map: measure every 6 inches across the tank to identify dead zones. Many reefers rent PAR meters from their local club. Apogee MQ‑510 is the gold standard. Do not rely on phone apps or lux meters – they cannot accurately measure PAR underwater.

📊 DIY PAR mapping: Draw a grid of your tank bottom and rock surfaces. Record PAR at each point. Adjust fixture mounting height or add supplemental lights for uniformity.

What Is the Best Light Spectrum for Coral Coloration?

A mix of violet (420 nm), royal blue (450 nm), blue (470 nm), and a small amount of white (5000–10000K) produces the best fluorescence and growth. Avoid excess red (>630 nm).

Different fluorescent proteins (GFP, RFP, Cyan) are excited by specific wavelengths: violet (420 nm) excites blue/green proteins, royal blue (450 nm) excites yellow/orange, and cyan (490 nm) excites red. Most high‑end reef LEDs (AI Prime, Radion, Kessil) provide 4–6 channels to tailor spectrum. Kessil A360X uses dense matrix LED to blend colors seamlessly. A recommended starting spectrum: violet 50%, royal blue 100%, blue 80%, white 20%, red 5%, green 5%. Increase white for a more natural daylight look, but too much white can dull fluorescence.

🔵 Violet (420nm)
Excites GFP, enhances blue/green pigments

🔷 Royal Blue (450nm)
Primary zooxanthellae peak, drives growth

⚪ White (5000-10000K)
Provides full spectrum for human viewing

How Long Should Reef Tank Lights Be On (Photoperiod)?

Total photoperiod: 10–12 hours including 1–2 hour ramp. Peak intensity (all channels) for 6–8 hours. A midday siesta is optional but can help control algae.

A typical schedule: 2h ramp (dawn), 8h peak, 2h ramp (dusk). For SPS‑dominate tanks, many keepers shorten peak to 6 hours but increase intensity. Melev’s Reef study found that extending photoperiod from 8 to 12 hours increased coral growth by 15% but also doubled algae growth. Use a siesta (e.g., 6h on, 2h off, 4h on) to disrupt algae photosynthesis without harming corals. Always include a moonlight period (1–2% intensity) for nighttime viewing and natural behavior.

Phase	Duration	Intensity (blue:white ratio)
Dawn (ramp up)	60 min	0% → 80% (mostly blue)
Peak (midday)	6–8h	100% blue, 50–80% white/violet
Dusk (ramp down)	60 min	80% → 0%
Moonlight	2–6h	1–2% (royal blue only)

What Are Signs of Too Much or Too Little PAR in Corals?

Too little PAR: corals turn brown (zooxanthellae overproduction) or stretch toward light. Too much PAR: bleaching, tissue retraction, burnt tips on Acropora, and fluorescent protein overproduction.

Observing coral behavior is key. Low light signs: SPS lose coloration (brown), LPS polyp extension decreases, and corals grow tall/skinny (etiolation). High light stress: bleaching (white skeleton), tissue retraction, burnt tips on Acropora, and excessive mucus production. Some corals may overproduce fluorescent proteins as a sunscreen, appearing extremely bright before bleaching. Advanced Aquarist research suggests that moderate high light (just below bleaching threshold) yields the best pigmentation. Always acclimate gradually.

🔍 Quick check: If your Acropora has white tips (not new growth) and polyps are retracted, lower PAR by 20% and reduce photoperiod by 2 hours.

What Are the Best Reef LED Light Brands?

Ecotech Radion (XR15/XR30), AI Prime 16HD/32HD, Kessil A360X/A500X, and Orphek Atlantik. For budget, Nicrew Saltwater and Noopsyche are decent options.

Premium brands offer app control, multiple channels, and high PAR. Ecotech Radion XR15 Pro G6 features diffusers for even spread and Mobius wireless control. AI Prime 16HD provides 6 channels and compact size. Kessil A360X is famous for natural shimmer and dense matrix LEDs. Orphek Atlantik has very high PAR and a wide spectrum. For smaller budgets, Nicrew Saltwater LED includes actinic and white channels with a built‑in timer. BRS buyer’s guide compares PAR maps for all major brands. Choose based on tank size, coral type, and your controllability needs.

📋 Official brand links (nofollow):
• Ecotech Radion
• AI Prime
• Kessil A360X
• Orphek
• Nicrew Saltwater

📚 Explore more reef lighting guides: ← Main Lighting Guide (T1) PAR for SPS/LPS/Soft Reef brand comparison Coral acclimation guide Refugium lighting DIY PAR mapping Bleaching prevention

📊 Coral PAR reference table

Coral type	Example species	Ideal PAR	Placement
SPS (Acropora)	A. millepora, A. tenuis	300–500	Top 1/3 of tank
SPS (Montipora)	M. capricornis, M. digitata	200–350	Mid to high
LPS (Euphyllia)	Torch, Hammer, Frogspawn	75–150	Middle or sand bed
LPS (Trachyphyllia)	Open brain, Scolymia	50–100	Sand bed, low flow
Soft corals	Zoanthids, Palythoa	50–150 (zoas up to 200)	Low to mid
Mushrooms	Rhodactis, Discosoma	30–70	Shaded or sand

📖 References & further reading
• Reefs.com – Coral PAR requirements
• NOAA – Coral reef light
• BRS – Acclimation guide
• Advanced Aquarist – PUR vs PAR
• Melev's Reef – Photoperiod effects
• BRS – Reef LED buyer's guide
• Apogee underwater PAR meter