Why Lighting Matters in Reef Tanks

In the wild, sunlight delivers the energy corals need to thrive. In your reef tank, lighting plays the same role—it powers photosynthesis in symbiotic algae (zooxanthellae) living within coral tissues. Without the right lighting, corals cannot produce the nutrients they need, resulting in poor growth, faded color, or even coral death.

Understanding how lighting affects coral growth is essential for reefkeepers of all levels—but especially for beginners aiming to establish a healthy, vibrant coral system.

How Corals Use Light: The Role of Photosynthesis

Corals host microscopic algae called zooxanthellae inside their tissues. These algae use light to perform photosynthesis, converting it into sugars and oxygen that nourish the coral. This relationship supplies up to 90% of a coral’s energy needs.

Without sufficient light, zooxanthellae cannot function properly. Corals will then struggle to grow, lose color, or become stressed. Too much light, on the other hand, can cause bleaching—a protective response that expels zooxanthellae and robs the coral of its nutrients and color.

In other words:
Too little light = starvation
Too much light = bleaching

Understanding PAR, PUR, and Spectrum

PAR (Photosynthetically Active Radiation)

PAR refers to the amount of usable light (400–700 nm) reaching the coral. This measurement indicates how much "photosynthesis‑useful" light your tank is receiving.

PUR (Photosynthetically Usable Radiation)

PUR is a subset of PAR—the portion of light that corals can actually use for energy. High PUR means corals don’t just see the light, they use it efficiently.

Light Spectrum and Coral Growth

Different wavelengths influence coral growth and coloration:

• Blue Light (420–500 nm): Promotes photosynthesis and fluorescence; essential for most corals.
• Violet (380–420 nm): Drives pigment expression and coloration.
• White/Full Spectrum (500–650 nm): Improves overall appearance but contributes less to photosynthesis.

In reef tanks, blue and violet spectrum light promotes the best balance of growth and coloration.

Matching Light to Coral Types

Not all corals require the same lighting. Here’s a breakdown by coral group:

SPS (Small Polyp Stony) Corals

Examples: Acropora, Montipora

• Lighting: High intensity
• Flow: Strong, randomized
• Why: SPS corals rely on intense light for photosynthesis and rapid skeletal growth.

LPS (Large Polyp Stony) Corals

Examples: Torch, Frogspawn, Candy Cane

• Lighting: Moderate to high
• Flow: Moderate
• Why: LPS corals depend on sufficient light for zooxanthellae function but prefer less intensity compared to SPS.

Soft Corals

Examples: Mushrooms, Zoanthids, Kenya Tree

• Lighting: Low to moderate
• Flow: Gentle to moderate
• Why: Soft corals are less reliant on intense light and thrive in softer spectrums.

Top Lighting Systems for Reef Tanks

Here are some of the most effective lighting systems for coral growth in 2025:

EcoTech Marine Radion G6

• Excellent PAR/PUR balance
• Customizable spectrum with ReefLink control

AquaIllumination Hydra 64HD

• Multi‑channel control for spectrum fine‑tuning
• Great coverage for mixed reefs

Kessil A360X

• Compact, customizable LED
• Deep blue spectrum ideal for corals

T5 + LED Hybrid Systems

• Broad, even coverage
• Often preferred for larger or SPS‑heavy tanks

Lighting Schedules and Coral Health

Most reefkeepers follow a photoperiod schedule that mimics natural sunlight:

• Ramp up (Sunrise): 1–2 hours
• Peak intensity: 6–8 hours (majority blue spectrum)
• Ramp down (Sunset): 1–2 hours
• Moon phase (optional): Low blue light overnight

This gradual light cycle reduces stress and supports natural coral behavior.

Signs Your Lighting Needs Adjustment

Watch for these common coral responses:

Too little light:

• Faded or dull coloration
• Limited growth
• Polyps not fully extending

Too much light:

• Bleaching or paling
• Tissue recession
• Corals retreating deeper into rockwork

Adjust intensity gradually and monitor coral response over days to weeks.

Tips for Lighting Success

• Test PAR/PUR at coral placement levels, not just at the surface.
• Prioritize blue spectrum during peak hours for optimal growth and fluorescence.
• Use controllable lighting systems for fine‑tuning.
• Balance light with flow and water quality for best results.

Conclusion: Light Is Life for Corals

Lighting does more than brighten your reef tank—it drives biological processes essential to coral growth and health. By understanding light spectrum, intensity, and scheduling, you can create an environment where your corals not only survive but flourish with vivid color and robust growth.