Properly lighting a reef tank is one of the most important considerations when planning a new aquarium or upgrading your lighting set-up.
There’s a lot of information to sift through if you’re looking for answers online. The science of light and corals is a very complex and can get confusing, especially when you looking for straight-forward information.
At Marine Depot, we get thousands of questions every month. Reef lighting is certainly at the top of the list!
We are commonly asked, “What type of lighting do I need for good coral growth?” and “Which lighting fixture is right for my tank?”
Although there can be a simple answer to these questions, it's important to understand the science that informs these decisions as well.
Pretty much everyone knows that light is critical for keeping SPS and LPS corals. Many new reefers tend to blast the corals with as much light as possible, which research on captive corals shows isn’t ideal. In the early days of reef-keeping, aquarists bought the biggest, brightest
lighting they could find. Everyone knew coral reefs thrived under direct sunlight. So, DIY reefers were trying to hang the power of a hundred suns over their tanks. That’s what the public aquariums were doing, so why not try the same thing at home?
But it didn’t always work. The lights over-heated the water, some corals stopped growing, and others were burned. When it came to light, more was definitely not better.
Today we understand a lot more about the lighting requirements of corals and other photosynthetic invertebrates. We tried to distill all this information down for you to make choosing a light less of a headache.
The major factors to keep in mind when looking for a light are wireless controllability, programming modes, and a sleek form. However, the king of all these factors is the light’s PAR, which is the first thing you should look at. PAR stands for Photosynthetic Active Radiation. It is the range of
light wavelengths used by symbiotic algae living inside coral tissue. PAR is the engine that drives photosynthesis and it’s photosynthesis that feeds coral.
If your lighting rig is bright but doesn’t provide the right light spectrum, all your doing is burning electricity. Quality beats intensity!
PAR covers the visible lighting spectrum but is heavy in the blue (400 – 500 nm) and red (600 – 700 nm) wavelengths. A light can be bright but not provide PAR. PAR is measured in “micromole photons per square meter per second” units. Thankfully there’s no math involved in figuring out a
fixture’s PAR rating. Most of today’s top LED light manufacturers provide PAR specs for their fixtures making life a lot easier. They get these measurements by using a PAR meter. The sensor is first placed in the water, under the light. Readings are then taken at various depths and distances
from the center of the LED array. PAR readings are plotted to show how the intensity of PAR drops as you move further from the light. You can use the manufacturer’s PAR data to get a rough idea of the amount of light your tank will receive with a particular light fixture.
You can also take your own measurements with a PAR meter. PAR meters are a little pricey, but they let you see PAR levels at different levels in your reef. It’s very helpful for determining where to best place your corals or make adjustment to the lights.
So what’s the right amount of PAR for corals?
Marine biologists have conducted PAR measurements on tropical reefs where SPS and LPS corals thrive. The PAR levels range from around 150 to over 450 across the world. But what level will satisfy most corals in a home aquarium?
Captive coral researcher Dana Riddle discovered that the ideal average PAR range for corals is 100-200 PAR. Too much PAR is both ineffective and actually inhibits photosynthesis, potentially damaging coral as well. 200-400 PAR will bring out vibrant coloration but sacrifices a little coral
growth. Research suggests the corals may even develop brighter pigments to protect against excess lighting.
The big takeaway is captive corals are happiest with moderate light intensity. Too much light will inhibit or harm the corals. There is no absolute rule on the perfect PAR for all corals, but a good starting point is 150 to 250 PAR.
So, how do you choose the right light fixture for your tank? Start by looking at the PAR specs. They’ll give you an idea of the maximum PAR at specific depths. There’s also nothing wrong with going with a more powerful fixture as long as you can dial it back, which is especially helpful as you
corals acclimate to a new lighting system.
If you can’t find PAR data for a particular light, search online and see how other aquarists are using the fixture. Learning from the experiences of others is always valuable.