The importance of lighting your reef aquarium - Red Sea

Why is lighting so important for your reef aquarium

Before we dive into common misconceptions about the lighting in reef aquariums, here are 4 reasons why lighting is so important:

1. Photosynthesis

The entire reef ecosystem depends on light. Why? Because light drives photosynthesis. 

We know that corals gain 80 to 85% of their energy needs through the process of photosynthesis that converts light energy into chemical energy.

So, if light drives photosynthesis – who’s the driver? Well, that would be zooxanthellae. These microscopic algae provide the energy of photosynthesis to the coral. That makes them the primary producers in this complex ecosystem.

2. Coral Growth

A specific range of the blue light spectrum is directly responsible for coral growth.

Our research into the photobiology of corals shows that a specific wavelength within the blue light spectrum significantly stimulates the creation of new calcification centers in the corals’ skeleton.

3. Coral Colors

Other segments of the blue light are directly responsible for coral coloration. They stimulate the production of the coral’s pigments, also known as chromoproteins, which at the end of the day, is what we’re all after – vivid and vibrant colors.

4. Hormone production & immune system

Light regulates growth, pigments, hormone production and even enhances the immune system activity in fish and other invertebrates.

Check out our ReefLEDs, the Reef-Safe lighting that deliver the precise light spectrum, intensity, and photoperiod that provide the optimal conditions for corals to flourish.

What makes aquarium lighting reef-safe?

In the context of lighting, REEF-SPEC means the tested specifications that are required by corals to flourish in an artificial environment, like your reef aquarium. So, REEF-SPEC, in a nutshell, is what your corals need.


Now, if you’re thinking: How does Reef-Safe even apply to lighting? Or: What’s the difference between REEF-SPEC and Reef-Safe? Well, that’s what this blog is here for.


We all know that what corals need and what reefkeepers want aren’t always the same thing. Sometimes, what pleases the eye, are the wavelengths, light intensities, or prolonged photoperiods that generate excessive energy.


This undesired energy source turns into heat, promotes the formation of toxic, free oxygen radicals, and damages coral tissue, zooxanthellae, and more.


That’s why we created the “Reef-Safe” standard for lighting that focuses on us as reef hobbyists. It reduces the risk of user errors, which may damage the corals. Red Sea’s ReefLED™ light allows us to set and change the lighting to suit our visual preferences, but still, be on safe grounds without harming the corals.


To determine exactly what meets both the biological and physiological needs of these amazing creatures, we conducted intensive research into the photobiology of corals. We were able to identify the specific light spectrum, light intensity, and photoperiod that provide the optimal conditions for corals to flourish.


These are our guidelines for creating optimal reef conditions in your aquarium, or what we like to call, REEF-SPEC.

Just to give you an idea, the optimal spectrum for coral growth and color expression, is between 360 to 480 nm (nanometers). We’re talking about UV and blue spectrum mainly, and not all of it is within the visible light range.


If your lights go above 480 nm into the greens, yellows and reds, you could even harm the corals. I’ll explain more about it in the following blogs.

Busting light measurement myths

I’m going to shed some light on PAR measurements. We all use PAR meters to measure light in our reef aquariums. But, is it possible that it’s obscuring part of our view?


The PAR measurement was developed for the terrestrial photobiology research of plants and crops. It represents the intensity of Photosynthetic Active Radiation within the visible light spectrum spanning between 400 to 700 nm (nanometers).


But the spectrum that is relevant for the corals starts below the range of the visible light in the UV region and continues into the blue part of the visible light range.

This section of the spectrum is between 360 to 480 nanometers and is the Photosynthetic Utilized Radiation or PUR that is actually used by the corals.


So, you can already see that using PAR measurements to determine the suitability of light for corals doesn’t tell us the whole story. On the one hand, the PAR measurement is missing an important part at the bottom end of the spectrum (360-400 nm). These wavelengths, in the UV range, below 400 nanometers, enhance coral growth and color expression and stimulate the auto-recovery process of photosynthesis.


And on the other hand, at the top end of the spectrum, any wavelength above 480 nanometers, meaning a significant part of the PAR measurement, that includes the green, yellow, and red wavelengths, cannot be utilized by corals.


In excessive amounts, these wavelengths may turn into heat energy inside the soft tissue of corals, which causes stress and photoinhibition.


You’re right if you think that the zooxanthellae can use the red end of the light spectrum, but they’re fine without it. And since these algae sit inside the coral’s soft tissue, the red light may damage the coral before it can be utilized by the zooxanthellae. Bottom line, our research shows we’re better off without it.


To sum it up, PAR tells us about the intensity of the full visible light spectrum, but it doesn’t tell us anything about the suitability of the light source for a reef aquarium.

PUR, on the other hand, tells us exactly what we need to know. 


Unfortunately, there are no coral PUR meters. To precisely measure PUR underwater, you need to use a special device like the Ocean Optics Radio Spectrophotometer we use during our research. It provides us the specific spectral irradiance for each individual wavelength which allows us to calculate the percentage of PUR from the regular PAR reading.

Based on our research, we recommend checking out the percentage of PUR from the PAR reading when evaluating or comparing lights for a reef aquarium.

Light intensity and photoperiod

I’ll explain about photoperiod, which is the third parameter of REEF-SPEC lighting. I’ll explore the relationship between photoperiod and light intensity and how it affects your reef.

Let’s start with the basics: 

Like every photosynthetic organism corals need light, but there’s only so much they can take. That means that the duration of the daily photoperiod is very important. Even the optimal amount of daily photosynthetic activity generates residual energy inside the coral that must be released, so they need a period of darkness, just as much as they need the light.


Our research has shown that to get optimal coral growth and coloration, light and dark periods should be about the same. Also, the intensity and photoperiod are inversely proportional, which means if one goes up, the other must come down and vice-versa. So, for a 24-hour daily cycle, we recommend approximately 12 hours of light with an average PUR intensity of between 100 to 450 micromoles, followed by 12 hours of darkness.


Moonlight should also be taken into account as part of the total daily light energy and therefore should either be at very low levels or be included as part of the photoperiod. Our research did not only give us these guidelines, but it also provided an insight into what is going on inside the coral.


We all instinctively understand that not enough light will limit coral vitality, but what about too much of it? Overexposure to light, meaning exceeding the maximum amount of energy that the corals can handle, has undesired effects. We’re talking about things like the formation of free oxygen radicals and the conversion of unutilized light energy to heat, both of which cause the accumulation of toxins in the coral tissues, and when they occur together, they make matters worse.


What you’ll see is the polyps and soft tissue retracting into the skeleton of the corals to reduce their exposure to light or paling of the soft tissue. These are the first signs of photoinhibition, and it’s the coral’s auto-protection mechanism kicking in. Fortunately, these effects are reversible, but prolonged overexposure may cause long-term damage.


If you don’t have REEF-SPEC lighting, then when setting up your aquarium lighting watch out for a few of the settings that can cause photoinhibition:


  • The wrong light spectrum – Set your lighting as close as possible to the coral PUR spectrum.
  • The right spectrum at a too high intensity – Avoid hotspots of over 450 PUR at the water surface.
  • The right intensity for too long a period – Apply the recommended photoperiod guidelines of about 12 hours of light and dark per day.


So, to recap: Like spectrum and intensity, the photoperiod has a significant impact on the health and vitality of your corals. 


And a quick tip, if you want to enjoy your reef a bit longer over the weekends, no problem, just increase the photoperiod but make sure you compensate by reducing the intensity for a few hours during the day.


Now, if you choose to use Red Sea’s ReefLEDs you don’t have to worry about getting it right, they’ve already been designed according to the spectrum and intensity guidelines we discussed in this article series. 


The photoperiod is up to you, and don’t worry about overdoing it, our ReefBeat App will let you know if you are about to go over the edge.