Lighting looks a little bit different in the marine world, and it is essential to know the basics before keeping corals. Jeremy is here to explain what you need to know.
Lighting is incredibly important for reef aquariums. Many of the corals we keep have symbiotic zooxanthellae algae in their tissues which generate energy from the light which the corals utilise to live and grow.
In the tropics, where coral reefs occur, sunlight is pretty much constant year-round, for 12 hours per day, every day. There will be storms, cloud cover and occasional rainfall, but our corals are adapted to receive intense light at some point every day and with a fixed day/night cycle. Corals even use moonlight too, not for energy, but for spawning.
Therefore, we must try to mimic the daily sunlight that reefs receive in our aquariums for corals to thrive. An we do that by utilising bright LED lighting.
Need help choosing your first saltwater tank? Read our Beginner's Guide To Reef Tanks: Choosing the Right Marine Aquarium.
Trumpet coral fluorescing under blue LEDs - Photo by Shutterstock
Why Do Reef Lights Look So Blue?
Sunlight appears white, but it's actually a spectrum of light going all the way from ultraviolet to infrared. White light is actually like a rainbow, containing violet, blue, green, yellow and red in a wide band.
When sunlight penetrates seawater, however, it is filtered by the water. The red wavelength is the first to be filtered out, while the blue wavelength is last.
Therefore, the blue light penetrates the deepest in seawater and it's that blue light that most of our corals, or more specifically their symbiotic algae, are adapted to use and benefit from.
That’s why marine lighting looks much bluer than freshwater lighting. It's better for the corals, and it looks really cool too. Some corals will even fluoresce under blue light, showing off neon greens, oranges, and pinks.
Red Sea ReefLED G2 can be suspended above an aquarium
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What Makes A Good Reef Light?
A good LED light will have the right spectrum and intensity of light to support healthy coral growth.
Ideally they will also have adjustable colours enabling reefers to have a warmer, white light if they are growing corals from shallower water, or a cooler, blue light for deeper water species. Violet and ultraviolet are important too, and they feature on premium reef lights, along with red to enhance colour, and green.
Brightness goes hand in hand with light spectrum and the sun is of course unrivalled in its brightness. Again, seawater lessens that brightness the deeper it gets, but corals still need much brighter light than the average aquarium light can provide.
Example of a PAR Diagram for the TMC AquaRay
Understanding PAR
Brightness is measured in Photosynthetic Active Radiation, or PAR, with the higher the par number, the brighter the light. Most of our corals inhabit a PAR band of around 100-300, with high light loving corals (like many SPS corals) experiencing more than this, and low light tolerant corals experiencing less.
If you provide lighting that is 300 PAR near the top of your tank and 100 PAR at the bottom, it will be perfect for a mixed reef. That's because you ca place corals on the rock structure according to their lighting requirements.
PAR meters are available but they aren’t necessary for beginners. The manufacturers spend years of testing their light units in order to recommend their lights by tank size.
Most LED lights are modular so a manufacturer may recommend one to light a 60cm (24”) cube, for example. If your tank is 120x60x60cm (48x24x24”), you would simply require two of these lights, for a tank that is 180x60x60cm (72x24x24”) you'd need to add a third.
Your local marine store should also be able to advise you the best lighting setup for your aquarium.
Related article: How do I cycle my new nano reef tank?
Can Reef Lights Be Programmed?
One of the biggest advantages of modern LED lighting is the level of control available.
Unlike older lighting technologies, today's reef lights can be adjusted for both colour and intensity throughout the day. Most systems connect directly to a smartphone or tablet, making setup and control incredibly straightforward.
Many reefkeepers use gradual sunrise and sunset effects, allowing the lights to ramp up slowly in the morning and fade down again in the evening. This creates a more natural environment for fish and corals while reducing stress caused by sudden changes in brightness.
Many lighting systems can also simulate:
- Moonlight cycles
- Cloud cover
- Storm effects
- Seasonal lighting variations
While all the features and controls are exciting, beginners are often best served by sticking with manufacturer-recommended settings. Corals thrive on stability, and constantly changing lighting programmes can sometimes do more harm than good.
Once you've found a setting that works, leave it alone and allow your corals time to adapt and grow.
Related article: Characterful blennies for your reef tank.
How Should I Mount My Reef Lights?
Most reef LED fixtures perform best when mounted approximately 20cm (8") above the water surface.
There are several ways to achieve this. Many manufacturers offer dedicated mounting arms that attach to the aquarium rim, while others provide suspension kits that allow the lights to hang from the ceiling.
D-D The Aquarium Solution Slimline Bracket
For larger aquariums, rail systems can be used to support multiple fixtures across the tank.
Two D-D Spektrums on Mounting Rail
One advantage of modular LED lighting is scalability. You may start with a single light over a small aquarium and simply add additional units if you upgrade to a larger tank in the future. Most lighting apps allow multiple fixtures to be grouped together and controlled as a single system.
Some manufacturers even integrate lighting control with pumps, automatic dosers, and other equipment, allowing much of the aquarium to be managed from one app — if you buy all the equipment from the same brand.
Do Reef Aquarium Lights Use A Lot Of Electricity?
Modern LED lighting is far more energy efficient than older reef lighting technologies, like metal halides.
A high-end reef light may have a maximum power rating of around 200 watts, but it rarely operates at full output for extended periods. Most reef aquariums run a lighting schedule of around 8-12 hours per day, with gradual ramp-up and ramp-down periods at the beginning and end of the cycle.
In addition, many reefkeepers run their lights at around 75% power rather than maximum intensity.
Compared with older T5 fluorescent systems or metal halide lighting, modern LEDs offer significantly lower running costs, while producing less heat.
Acropora require intense lighting - Photo By Shutterstock
Which Reef Light Is Right for Me?
For most beginners, the simplest way to choose a reef light is to follow the manufacturer's recommended tank coverage guidelines.
Start by measuring your aquarium's length and width, then select a light or combination of lights designed to cover that area. It's generally better to invest in a quality light with sufficient output than to choose a cheaper unit that struggles to provide the spectrum and intensity your corals require.
Remember that powerful lights can always be turned down if necessary. Underpowered lights, however, may never provide the conditions required for long-term coral health and growth meaning you'll likely upgrade them after a short while.
If you're unsure, speak to your local fish shop. Many retailers have reef lighting running over displays tanks and coral trays. They will be able to demonstrate the different options available, helping you choose a system that suits both your aquarium and the types of corals you plan to keep.
Get the lighting right from the start, and you'll be giving your corals one of the most important ingredients they need to thrive.