It is widely known that corals need proper lighting to grow. But illuminating a reef tank is pretty challenging, as there are many factors to consider.
Which types of corals require higher light intensities than others? Which color should I choose? How do I adjust the intensity?
Since I have faced all these questions in the past, I decided to gather all the essential information in one place.
So, without further ado, let’s dive right into it.
What Kind Of Light Do You Use For Corals?
Quick Answer: Better to go with LEDs, as they are energy efficient, durable, and don’t affect the water temperature.
The lighting type is just as important as the light color.
Although, you can use any one of the following lighting types to rear corals in a reef tank successfully if the intensity and photoperiod are correct:
1. LEDs (Most Recommended)
LEDs are the most prominent lighting option on the market today. First of all, this lighting type is extremely efficient.
LEDs emit light in every direction while wasting very little energy. They don’t influence the water’s temperature.
Secondly, LEDs are long-lasting. You can run them for 100,000 hours or more.[1] Third, LEDs are easy to maintain and upgrade.
If you had to make a decision at this moment, LEDs are unquestionably the superior choice among the various lighting systems.
The LEDs I just at the moment are the Hygger 24/7 Aquarium LED Light (link to Amazon). It is highly affordable and easy to use.
You can either use the default mode, which uses both white and blue light at different times of the day, or the DIY mode, in which you set your own preferences.
2. Fluorescent
Most aquarists start with fluorescent lights when they first experiment with aquariums. This lighting type is long and thin, and it spreads the light over a large area.
Fluorescent lights are affordable and easy to operate. You will find them in various sizes.
While corals can grow under regular fluorescent bulbs, many aquarists combine them with metal halide lamps to satisfy corals with varying lighting requirements.
3. Metal Halide
You can find metal halides in color temperatures ranging from 3000 to 20000K. You can also find them in 150, 250, and 400 watts.
For the longest time, metal halides were the only answer to corals with intense lighting requirements. But then T5 fluorescent bulbs came along.
Even though they produce more heat than aquarists would like, you find them in reef tanks because they can stimulate growth in all coral types.
4. T5 High-Output Fluorescent
These are skinny tubes with a higher output than regular fluorescent lights. You get the same wide and even spread and a variety of colors.
In fact, you can buy full-spectrum T5 lighting systems.
Besides producing less heat than metal halides, T5 lamps are easier to upgrade.
They are also cheaper than LEDs and metal halides. However, you must change the bulbs every 9 to 12 months.[2]
5. Hybrid
You can combine multiple lighting types to produce a superior lighting system.
For instance, an LED/Fluorescent amalgamation gives you the versatility of a fluorescent bulb and the efficiency of an LED lamp.
But hybrids are usually expensive.
What Color Light Should I Use In My Coral Tank?
Quick Answer: If you had to choose one color, blue is the best for coral. However, many aquarists use white during the day and blue towards night.
You should match each lighting type with the correct color to optimize a coral’s growth. Your options include the following:
1. Blue (Most Recommended)
Blue is the best color light for corals because it stimulates higher photosynthetic rates in zooxanthellae.
These microorganisms (inside the coral’s tissue) use photosynthesis to produce nutrients for the corals. They have a stronger response to blue than any other color.
2. White (Usually Combined With Blue)
Many aquarists use white because the color mimics the sun. It gives the reef tank a natural look.
You can trust a white light to stimulate coral growth because it contains all the colors, including blue and violet.
It is common practice to combine white and blue.
Aquarists will use white light to illuminate the reef tank during the day, only switching to blue (or red) when the sun sets.
Blue allows you to see the tank’s contents without disturbing the fish.
3. Red
People routinely compare blue to red because both colors can stimulate photosynthesis in zooxanthellae.
Red (601 – 700nm) has a longer wavelength than blue (431 – 480nm). Not only does red attenuate quickly, but it delivers less energy than blue.
In a natural water body, the reds will disappear as you descend. Eventually, only blue will remain.
But in an aquarium, the depth doesn’t matter. You can substitute blue with red without harming the corals.
Admittedly, blue does a better job of making a coral’s colors pop.
4. Violet
At 400 – 430nm, violet has a shorter wavelength than blue. The pigments in zooxanthellae have a stronger response to violet than even blue.
It also penetrates deeper and delivers more energy. If you can only choose one color, violet is the best.
5. Green/Yellow/Orange
Red, orange, and yellow are the first colors to attenuate when sunlight strikes the water.
Aquarists usually reduce the greens, yellows, and oranges in a full-spectrum light because the colors have little or no biological benefit.
At the very least, removing green, orange, and yellow from a tank won’t harm the corals in the long run.
You can keep these colors if you like their impact on the coral’s appearance. Otherwise, they don’t matter to the photosynthetic process in zooxanthellae.
How Long Do You Have To Leave The Light On For Corals?
Quick Answer: A reef tank with corals requires 9 to 12 hours of light.
The intensity matters. You can lower the photoperiod at the highest intensity. These days, aquarists use adjustable lights.
Rather than suddenly switching the lights on or off, they will gradually ramp up and ramp down at dusk and dawn.
This protects the reef tank’s inhabitants from unnecessary stress. The corals don’t mind. However, fish hate unexpected change.
Therefore, you are more likely to harm them by suddenly turning the lights on and off. Keep in mind that light in the wild changes gradually.
You can follow this schedule if you’re only using white or blue light:
| 10 am | Light on (20 percent) |
| 12 am | Increase light to 50 percent |
| 1 pm | Increase light to 75 percent |
| 2 pm – 8 pm | Light is at full (100 percent) intensity |
| 9 pm | Decrease intensity to 60 percent |
| 10 pm | Decrease intensity to 20 percent |
| 11 pm | Shut lights off |
You can follow this schedule if you wish to combine blue with white:
| 9 am – 10 am | White light (20% intensity) |
| 10 am – 11 am | White light (50% intensity) |
| 11 am – 12 am | White light (75% intensity) |
| 12 am – 6 pm | White light (100% intensity) |
| 6 pm – 11 pm | Blue light |
| 11 pm | Lights Off |
And if you want to use other colors, such as red, violet, and green, all you have to do is activate that color instead of blue (between 6 pm to 11 pm).
How Do I Adjust The Light Intensity For My Coral?
Quick Answer: LPS corals require a PAR (Photosynthetically Active Radiation) range of 50-150, whereas SPS corals need a PAR range of 20-250.
Once you have chosen the lighting hours for your corals, the next step is to determine what light intensity they need.
For that, you’ll need a simple PAR meter. Basic devices can cost anywhere from $30 to $150, while more advanced models can cost upwards of $500 or more.
For starters, you can go for a relatively inexpensive model like the BTMETER BT-881E Digital Light Meter (link to Amazon).
Next, you will need to categorize your coral into one of two groups: SPS corals or LPS corals. This is what each category needs:
- LPS Corals: LPS corals generally require lower light levels, with PAR ranges typically falling between 50-150.
- SPS Corals: SPS corals require high to very high light levels, with PAR ranges typically falling between 200-450 or higher depending on the species.
For a better understanding, here is a great YouTube video by Fragbox Corals that explains how to measure the PAR level in your reef tank:
And if you are uncertain about the type of coral you have, here is a table where I have compiled a list of commonly found species in reef tanks:
| Coral Name | Recommended PAR Range |
| Staghorn Coral (Acropora millepora) | 300-450 PAR |
| Digitate Montipora (Montipora digitata) | 300-450 PAR |
| Bird’s Nest Coral (Seriatopora hystrix) | 300-450 PAR |
| Cat’s Paw Coral (Stylophora pistillata) | 300-400 PAR |
| Cauliflower Coral (Pocillopora damicornis) | 200-400 PAR |
| Hammer Coral (Euphyllia ancora) | 150-250 PAR |
| Moon Coral (Favia sp.) | 150-250 PAR |
| Candy Cane Coral (Caulastrea furcata) | 150-250 PAR |
| Lobed Brain Coral (Lobophyllia hemprichii) | 150-200 PAR |
| Sun Coral (Heliofungia actiniformis) | 100-200 PAR |
| Merlet’s Coral (Blastomussa merleti) | 50-150 PAR |
| Florida Mushroom Coral (Ricordea florida) | 50-150 PAR |
| Chalice Coral (Echinophyllia sp.) | 50-100 PAR |
| Zoanthids Coral (Zoanthus sp.) | 50-100 PAR |
How Do I Know If My Corals Are Getting Enough Light?
You can tell that your coral is getting enough light by observing their growth and coloration.
They will present vibrant colors and consistently grow over time. You will also see that their polyps and tentacles extend during the day.
On the other hand, if your coral gets too much light, you may notice the following symptoms:
- Bleaching – The coral will lose its color as it fails to live in symbiosis with zooxanthellae.
- Tissue recession – Your coral will expose its skeleton by retracting its tissues.
- Reduced polyp extension – The coral’s tentacles won’t extend fully, which impairs feeding and growth.
- Change of position – New corals will respond by moving away from the light source.
In the wild, intense light kills corals because it raises the water’s temperature, compelling the corals to expel their zooxanthellae.
Because corals cannot survive without these microorganisms, they will eventually die.
You don’t resolve this issue by reducing the light intensity to unsafe levels. After all, zooxanthellae use light for photosynthesis.
Low-intensity lighting will deprive the corals of vital nutrients, turning them brown in the process.
It is worth noting that insufficient or excess lighting does not guarantee a coral’s death.
First of all, some corals can tolerate various light intensities. A prominent example is Platygyra sinensis.[3]
Secondly, corals can acclimate to high and low-intensity lighting. Although their colors will deteriorate.
Can Corals Be Left With The Light On All Night?
No, you shouldn’t leave the light on all night. Studies have already determined that artificial lights at night are a threat to corals in the wild.[4]
This shows that corals require a period of darkness to survive. Aim for at least six hours of darkness.
Corals can tolerate blue light at night because it mimics moonlight. However, they can also survive without it. Corals don’t need blue light at night to grow.
Can Corals Survive Without Light?
No, corals cannot survive without light.
This is because they get their nutrients from zooxanthellae, and zooxanthellae are photosynthetic. Their survival is dependent on light.
Admittedly, experts have discovered deep-sea corals in the wild that live at depths where sunlight cannot reach them.
They survive by eating tiny organisms that passing currents trap and carry.[5] But obviously, these are the exceptions.
Conclusions
If you’re in a hurry, here’s a quick rundown of the key points mentioned above:
- The type of lighting used is important for coral growth in a reef tank, and LED lighting is recommended due to its energy efficiency, durability, and lack of impact on water temperature.
- The color of the light is also important, with blue being the most recommended for corals as it stimulates higher photosynthetic rates in zooxanthellae.
- Combining different lighting types can create a superior lighting system, such as combining fluorescent and LED lights.
- White light can be used during the day and blue light at night to simulate natural lighting patterns and optimize coral growth.
- A reef tank with corals requires 9 to 12 hours of light, with the intensity of the light also being a crucial factor.
References
- https://www.stouchlighting.com/blog/led-lights-versus-metal-halide
- https://www.atinorthamerica.com/blog/how-do-i-replace-t5-bulbs-and-how-often-should-i-do-it/
- https://www.sciencedirect.com/science/article/pii/S0272771419304652
- https://www.southampton.ac.uk/news/2018/12/artificial-light-coral.page
- https://ocean.si.edu/ecosystems/coral-reefs/deep-sea-corals