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Coral Reef Lighting Guide

Recommended photoperiod and PAR levels for your corals

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In order to grow healthy and vivid corals, it is crucial to provide your reef tank with the proper spectrum, intensity and duration of light. Measuring photosynthetically active radiation (PAR) is crucial in assessing the quantity and quality of light for plants. PAR is not only the most important measure of light in terrestrial photobiology research for plants and crops, but also for underwater plants such as corals and other reef plants.

Reef Lighting

The entire reef ecosystem depends on light for photosynthesis, which is the process where corals derive 80-85% of their energy from. Furthermore, reef lighting stimulates the corals' chromoproteins that are responsible for creating beautifully vivid and vibrant colors within your reef aquarium.

Color: The Light's Spectrum

As most corals originate from deeper waters where most yellow and red light is filtered by the water, they usually grow and look best under light with a blue coloration. The light color that a lamp produces is measured as the correlated color temperature (CCT) in kelvin. The higher the kelvin value, the more blueish the light gets. It is common for reef aquariums to use lighting ranging from around 6500 K up to 20000 K.

PAR Level Recommendations

Providing your corals the proper PAR / PPFD levels are crucial in order to keep them growing healthy.

As corals are very resilient to different light levels, individual types are capable of adapting to a wide variety of light levels given enough time for acclimation to changes in intensities. Only focusing on PAR values might be dangerous as corals require careful observation and adjustments based on their individual needs and reactions.

Mind that PAR levels are measured as photosynthetic photon flux density (PPFD) in the unit of µmol/m²/s.

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 PAR values, a good starting point is to limit the photoperiod to about 9 hours. If your aquarium runs at the lower range of PAR levels, extending the light period to up to 12 hours is probably better.

Signs For Too Much Light

Losing Color

If your corals start losing color, you may want to reduce the light intensity or reposition them to a lower or outward section of your reef aquarium and carefully observe how the corals react. Turning pale or going completely white is the most common reaction to too much light.

Reducing Size

Another sign of too much light is that the coral itself is shriveling instead of keeping or extending its size. This might or might not happen in conjunction with a loss of color as well.

Signs For Too Little Light

Turning Brown

If your corals start to turn brown, this might be a sign that they require higher light intensities. Mind that this is also a common reaction to suboptimal water quality that needs to be observed as well.

Slow Growth

If your coral is not growing as you expected, this might be a symptom of too little light or also way too much light. In this case it might be best to measure detailed light intensities and research for others' lighting experience what your specific coral.

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