Marine / Reef LED Light Guide
How reef-grade LED fixtures deliver the blue/actinic spectrum and PAR that corals need, with guidance on intensity, spectrum, and acclimation.
What it is
A marine or reef LED light is a high-intensity fixture designed to support photosynthetic corals in saltwater aquariums. LED fixtures are generally the most efficient aquarium lighting type and produce less heat than metal halide lamps, while offering programmable schedules and dimming.
Why corals need it
Corals host symbiotic algae called zooxanthellae, which photosynthesise and supply much of the coral's nutrition. Light in the 400–500 nm range is most beneficial for these photosynthetic organisms, and the shortwave portion of about 400–450 nm is most useful for coral coloration. Light in roughly the 400–450 nm band is commonly called actinic light.
Spectrum
Reef LEDs combine white channels with strong blue and actinic emitters. The strongest coral fluorescence is observed in the 400–450 nm range. Research has reported that blue light around 440–470 nm and violet light around 400–430 nm can increase protein content and growth in some corals.
PAR and intensity
Light intensity for corals is measured as PAR (photosynthetically active radiation). Many soft corals and LPS are well served by roughly 200–300 µmol photons m⁻² s⁻¹ (about 10,000–15,000 lux), which can be enough to saturate photosynthesis. SPS corals such as Acropora demand more, with reported targets around 600–700 at the top of the water column and 200–300 lower down and in the corners.
Placement and acclimation
- Establish a PAR gradient so SPS sit higher and soft corals and LPS sit lower in the tank.
- When mixing types, SPS are usually limited to the top half or third of the tank.
- Increase intensity gradually, since more light is not always better and some corals can be over-lit.
- A common belief among hobbyists that a tank cannot be over-lit, especially for SPS, is not supported for all coral types, so a gradient suits the differing needs of the species kept.
Advantages over older lighting
LED fixtures produce very little heat compared with metal halide, which reduces the need for chillers and added cooling. They are highly efficient: leading LEDs exceed 200 lumens per watt, and LED lamps typically last about 15,000 to 50,000 hours. They are also dimmable when the driver supports it, which is why pure LED systems have become common over reef aquaria, though early adopters noted that a limited spectrum could affect coral growth, a concern addressed by modern multi-channel fixtures.
Sizing
Reef LED fixtures are commonly used over saltwater tanks of roughly 100 litres and larger. Programmable controllers allow daily schedules, gradual ramping, and lunar simulation, which support stable conditions for coral growth and help corals acclimate to changes in intensity.