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Coral Reef Lighting

PPFD and CCT recommendations, plus how to spot and avoid common lighting problems

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Proper lighting is crucial for healthy coral growth and vibrant coloration in reef aquariums. Two key measurements are essential for managing your corals' light exposure: PPFD and CCT.

If you're unsure what these terms mean, take a look at the following article:

Measurement Values Explained

Learn about PAR, PPFD, DLI, Illuminance, and CCT

Photone - Grow Light MeterDennis Briner

Controlling PPFD and CCT in Aquariums

Understanding and managing both PPFD and CCT allows you to optimize your aquarium's light environment for coral health and growth.

Controlling PPFD

PPFD measures the intensity of light reaching your corals at any given moment. You can adjust PPFD in two main ways:

Mounting Height: Adjusting the distance between your aquarium light and the corals affects PPFD. Moving the light closer increases PPFD, while moving it farther away decreases PPFD. However, be cautious of heat buildup when placing lights too close to the water surface.

Dimming: Many modern aquarium LED lights have built-in dimming features. Reducing the dimmer intensity directly lowers the PPFD. This method allows for precise control without changing the light's position.

Controlling CCT

CCT represents the color temperature of the light, measured in Kelvin (K). In reef aquariums, CCT typically ranges from 6,500K to 20,000K. You can adjust CCT in several ways:

Light Selection: Choose fixtures or bulbs with the desired CCT. For example, 10,000K to 14,000K is often a good starting point for many coral species.

Multi-Channel LED Systems: Many modern LED fixtures allow independent control of different colored LEDs (e.g., white, blue, red). By adjusting the intensity of these channels, you can fine-tune the overall CCT.

Programmable Settings: Advanced LED systems often include preset or customizable spectral settings, allowing you to adjust CCT throughout the day to mimic natural light cycles.

PPFD Level Recommendations

Providing appropriate light intensity is crucial for healthy coral growth. Here are general PPFD recommendations for different coral types:

It's important to note that these are general guidelines. Corals exhibit remarkable adaptability to various light intensities, given sufficient time for acclimation. Factors such as species, color morphs, and prior light exposure can influence a coral's light requirements.

While PPFD values provide a useful starting point, they shouldn't be the sole focus of coral care. Careful observation of each coral's health, growth patterns, and coloration is essential. Adjustments to lighting should be made based on individual coral responses and needs.

Ensuring the Proper Photoperiod

As corals are photoperiodic – meaning that they respond to the relative lengths of light and dark periods – it is crucial to maintain proper, natural lighting times. If you run with higher PPFD levels, a good starting point is to limit the photoperiod to about 9 hours. If your aquarium runs at the lower range of recommended PPFD levels, extending the light period to up to 12 hours is probably better.

Signs of Lighting Issues

Monitor your corals for these indicators of lighting problems:

Signs of Too Much Light

Bleaching

• Symptoms: Corals turning white or very pale, losing their color.
• Note: Often a stress response to excess light, but can also be caused by other environmental factors.

Tissue Recession

• Symptoms: Coral tissue pulling back from the skeleton, exposing white areas.
• Note: Commonly seen in SPS corals when light intensity is too high.

Polyp Retraction

• Symptoms: Coral polyps remain closed or retracted during daylight hours.
• Note: While some retraction is normal, prolonged retraction can indicate light stress.

Color Changes

• Symptoms: Corals developing unusually bright or fluorescent colors.
• Note: While vibrant colors are often desirable, extreme color changes can be a sign of stress.

Reduced Growth

• Symptoms: Corals show slower than expected growth rates or stop growing entirely.
• Note: Excessive light can cause corals to divert energy to protective mechanisms rather than growth.

Signs of Too Little Light

Elongation

• Symptoms: Corals stretching or growing in unusual patterns, often towards the light source.
• Note: Most common in SPS corals, which may develop thinner, more fragile branches.

Loss of Color

• Symptoms: Corals becoming pale or brown, losing their vibrant colors.
• Note: Different from bleaching, this is often due to increased zooxanthellae as corals try to capture more light.

Reduced Polyp Extension

• Symptoms: Coral polyps not extending fully or as frequently.
• Note: Polyps may extend less to conserve energy in low-light conditions.

Slow Growth or Tissue Recession

• Symptoms: Corals growing more slowly than expected or showing signs of tissue loss.
• Note: Insufficient light can lead to reduced calcification and overall health decline.

Susceptibility to Algae Overgrowth

• Symptoms: Increased algae growth on or around corals.
• Note: Slower-growing corals in low light may struggle to compete with algae.

Regular monitoring with Photone can help you maintain optimal light levels and avoid these issues. Adjust your lighting setup based on both measurements and visual cues from your corals.

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