Is Green Light Good For Corals? (5 Surprising Facts)

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Corals are known to benefit from blue light, as it penetrates the water effectively and allows zooxanthellae to perform photosynthesis.

However, less is known about other colors such as green. How do corals react to this color? Can aquarists use it in their reef tank?

These are questions I asked myself all the time when I first started this hobby. Today, I will share everything I know about this topic.

**A beautiful coral illuminated with green light**

Is Green Light Good For Corals?

Green light can induce photosynthesis in zooxanthellae, which are symbiotic algae in coral tissues that provide nutrients to corals. While green light is not as important as blue and red light for photosynthesis, it still has some benefits.

Some aquarists answer this question by arguing that green light is not bad for corals. In other words, it brings nothing beneficial to the table, but neither does it harm corals.

They base this conclusion on the idea that green and yellow lights are useless to the growth of the algae that corals host.

Corals in the wild prefer colors with shorter wavelengths. Not only do they penetrate deeper, but they have more energy. This is where the blue color shines.^[1]

When sunlight hits a water body, the water will absorb all the other colors except for blue.

This makes colors like yellow, orange, and green irrelevant to a coral’s growth. These creatures have evolved to photosynthesize in blue light.

Even if the color’s wavelength wasn’t an issue, people usually dismiss green in conversations about photosynthesis because green plants and organisms reflect it.

In other words, green color cannot participate in a photosynthetic organism’s growth.

But don’t be so quick to write green off. Green isn’t quite as useless as some people suggest. Consider the following:

1. Understanding The Symbiosis Corals Have With Zooxanthellae

First of all, you need to understand how corals work. Corals are animals living in a skeletal framework. They can’t photosynthesize.

While corals can capture drifting food in the water, they primarily extract their nutrients from zooxanthellae, symbiotic algae in their tissues.^[2]

You provide adequate lighting to reef tanks because, unlike corals, zooxanthellae can photosynthesize.

This makes them reliant on light. Under the correct lighting conditions, they will generate sugars that coral polyps use.

But this relationship is not one-sided. The corals protect the algae. These organisms need one another. Most corals will die without zooxanthellae and light.

**Even in reef tanks, Zooxanthellae are found within the coral tissues**

2. Green Light Can Enduce Photosynthesis In Zooxanthellae

Now that you know why zooxanthellae matter, the question you need to answer is whether or not green light can trigger photosynthesis in these organisms.

Many aquarists will respond with a resounding no because they have been told for years that plants don’t use green light for photosynthesis. They reflect it.

However, that is more of a myth than a definitive fact. The information surrounding green light and its role in a plant’s growth has changed:

First, you’re not wrong. Plants will reflect green light. However, they only reflect a small percentage.

Plants absorb most of the green light they receive (85 percent).^[3] It is still the least efficiently used color on the visible spectrum.

Nonetheless, it isn’t completely useless. Or, at the very least, organisms don’t waste the color by reflecting most of it.

Some experts have questioned the suggestion that chlorophyll absorbs green light poorly, which is why the color is not useful for photosynthesis.

They argue that tests analyzing chlorophyll’s ability to absorb green light use extracted or purified chlorophyll instead of an intact leaf.^[4]

Additionally, they disregard other pigments that also use light for photosynthesis. Some of those so-called accessory pigments absorb green light.

These two articles support this claim:

Jun Liu and Marc W. van lersel (University of Georgia, Athens, Horticultural Physiology Laboratory) revealed in a paper (Frontiers in Plant Science) that green light penetrates deeper in leaves to excite chlorophyll.^[5]
Ichiro Teerashima, Takeshi Inoue, Riichi Oguchi, Takashi Fujita, and Wah Soon Chow (Plant Cell Physiology) clarified that the green range in a strong white light would penetrate deeper into a leaf than red and blue.^[6]

When the lower chloroplasts absorb additional green light, it increases photosynthesis more significantly than additional blue and red light.

**Although it is quite rare, some aquarists use green light in their reef tank**

3. Corals Use The Green Color To Attract Zooxanthellae

By now, you’ve probably concluded that green isn’t that important. Yes, it improves a coral’s aesthetic value, but blue will do a better job.

Yes, green can stimulate photosynthesis, but again, blue, red, and white are far superior in that department.

With that in mind, why do researchers care about green? You can blame the zooxanthellae.

Corals can’t survive without zooxanthellae. Corals get some zooxanthellae from their parents (30 percent). They use a green glow to attract the rest.

Corals cannot move. Therefore, they can’t go hunting for these organisms. So instead, they emit a green fluorescent light that attracts the algae.^[7]

Admittedly, this green light comes from the corals. You can’t bathe corals in green light from exterior sources to attract zooxanthellae.

That being said, it is worth noting the vital role green light plays in a coral’s relationship with zooxanthellae.

4. Green Makes Corals Look Beautiful

People that dismiss green’s relevance usually appreciate the color for its aesthetic value. It will improve a coral’s appearance.

Interestingly, researchers have found that corals have a green fluorescent protein that uses blue light to produce a green light.^[8]

Blue light gets all the praise in this situation.

However, you can also use green light to make the coral’s appearance pop. It makes the reef tank look more natural.

5. The Depth Factor Doesn’t Play A Role In Aquariums

The depth argument doesn’t matter here because aquariums are too shallow to absorb green light.

Therefore, you don’t have to worry about tank water dampening a green LED’s impact by attenuating the light.

**Green light can make corals glow, but blue does a much better job**

How Long Do Corals Need Green Light?

You don’t have to restrict your tank to one color. You are better off installing LEDs that generate a full spectrum.

You can adjust each color’s intensity based on the reaction you’ve observed from the corals.

There’s no reason to prioritize green when corals grow best under blue. In the absence of blue light, red is still the superior alternative.

As always, you should aim for 8 to 12 hours of light, followed by a period of darkness. Leaving the lights on all night will disturb your corals.

If you have LEDs, you can raise and lower the intensity gradually at the beginning and end of each day. In other words, your schedule will look something like this:

8 am – 10 am	Light at 20 Percent
10 am – 11 am	Light at 50 Percent
11 am – 12 am	Light at 75 Percent
12 am – 8 pm	Light at full intensity (100 Percent)
8 pm – 9 pm	Light at 60 Percent
9 pm – 11 pm	Light at 20 Percent
11 pm – 8 am	Lights Off

Naturally, you should adjust these times based on when you sleep and wake up.

For instance, you can switch the lights off at 9 pm if that is your bedtime. You can also switch them on at 7 am if you’re up by that hour.

Additionally, some aquarists deploy green as a nighttime light instead of blue or red. They use the color to see their fish at night without disturbing them.

Excellent YouTube video explaining the ideal reef tank lighting schedule

Does Green Light Make Corals Glow?

The corals won’t necessarily glow, but you can make their colors more vivid and attractive with green lighting.

This will mostly improve the green and yellow parts of your coral. If the particular coral you are growing does not have these colors, you will not benefit from the green light.

Either way, blue is still the best option. This makes the corals glow and benefits them nutritionally. Corals can use blue lighting to emit a green and red glow.

Pro Tip: Feeling uncertain about how to light your coral tank? Don’t worry, I’ve got you covered with my ultimate guide on the topic.

Conclusions

If you’re in a hurry, here’s a quick rundown of the key points mentioned above:

Green light doesn’t harm corals, but it doesn’t bring any benefits to the table.
Corals in the wild prefer shorter wavelengths, like blue light, as they penetrate deeper and have more energy.
Corals extract their nutrients from zooxanthellae, which can photosynthesize and generate sugars that corals use.
Despite the common belief that green light is not useful for photosynthesis, it has been found that green light can penetrate deeper into leaves, increasing photosynthesis.
While blue light is preferred for stimulating photosynthesis, green light is appreciated for its aesthetic value and can improve a coral’s appearance. The green light is also used by corals to attract zooxanthellae.