Fish need light to survive. It helps them grow and keeps their immune systems healthy, preventing diseases and harmful conditions. Without sufficient light, they could become sick or die.
Fish need about 8-12 hours of light a day. Natural sunlight is best, but direct sunlight will cause the water to overheat and the algae to grow too quickly. It can also give your fish sunburn. Planted tanks require more sunlight, as plants and beneficial algae use it for photosynthesis. This provides fish with the oxygen they need to stay alive. They also get vitamin D by nibbling on the plants, keeping them healthy and their scales bright and vivid.
If your tank gets enough natural sunlight, you won’t need as many artificial lights. However, fluorescent bulbs and LEDs can help if your home’s a little dark. Emulating natural conditions is always best, so research how much light your fish get in the wild to keep them healthy.
How Much Light Do Fish Need?
As described by Aquaculture and Fisheries, all fish need an element of light to be strong and healthy. Without it, they’d die. Getting the right lighting involves more than simply illuminating the tank so you can see it properly. And it’s not just fish that benefit from lighting, but plants and beneficial algae also need light for photosynthesis so they can grow. Lighting is measured in the following ways:
- Wattage, which is the amount of energy used.
- Kelvin, which is the color of the lighting. Low is warm, high is cool. For context, natural sunlight at noon has a rating of 5500 Kelvin.
- Lumens, which is the brightness as perceived by the human eye.
- PAR, also known as photosynthetically active radiation, is the light that helps plants and beneficial algae grow.
When it comes to how much lighting your tank needs, it all depends on how many plants you have. All tanks need some plants to provide oxygen and hiding spots for the fish in the aquarium. Some plants have higher lighting demands, while others have less.
Standard freshwater planted tanks require around 8-12 hours of light a day, while reef tanks need approximately 10-12 hours of light. Because sunlight isn’t available for 12 hours of the day, aquarium lighting must provide this. More specifically, the following lighting requirements are a helpful guide to follow:
- Tanks with plants: 6500 to 7500 Kelvin, 15-30 PAR for low light plants, 30-80 PAR for medium light plants, or 80+ PAR high light plants.
- Fish only tanks: 5500 to 6500 Kelvin to illuminate the tank for viewing.
- Marine reef tanks: 300-500+ PAR for soft and hard corals.
What Happens If There’s Too Much Light in the Tank?
While not enough light can be harmful to the organisms living inside the aquarium, too much is also bad, as it can cause algae to overrun. This can:
- Reduce the amount of oxygen available
- Cause harmful spikes of ammonia
- Make the tank dirty and unclean
Fish also need a 12-hour period of darkness to sleep. As soon as the lights go out, they stop swimming to conserve their energy. If fish are exposed to too much light, they become tired, and their sleeping patterns become disrupted, making them stressed, tired, and anxious. Stress causes health and behavioral problems, including:
- Decreased appetite
- Diseases, such as ich
- Jumping out of the tank
- Poor scale quality
- Weight problems
Similarly, as described in a journal by Aquaculture, intense light can be stressful, causing the same issues as mentioned above. Too much light also heats the tank, making the water too warm.
What Happens If There’s Not Enough Light in the Tank?
If you don’t provide enough light in your aquarium, your plants and fish will suffer. Fish become pale, lethargic, and slow-moving, while plants struggle to photosynthesize. This means they’ll die, and the tank’s oxygen levels will deplete. As a result, you might notice your fish:
- Gasping for air at the surface
- Refusal to swim
- Loss of appetite
- Labored breathing
Why Do Fish Need Light?
Sunlight has several benefits for both the fish and plants in the tank. Without it, no living organism can survive for too long. That’s why you need to place your tank somewhere that gets plenty of filtered sunlight and use aquarium lights for all the times throughout the day it’s dark. Light has the following benefits for fish:
As described by the Florida Department of Agriculture and Consumer Services, plants produce oxygen as a by-product of photosynthesis. This is vital for a fish’s survival as they consume dissolved oxygen through their gills. Without it, they’ll suffocate and die.
The same journal describes how oxygen levels within an aquarium are at their lowest in the morning after the lights have been out for around 12 hours, highlighting how important light is for oxygen creation. If you leave your fish tank in a dark corner of your home without artificial lights, your fish will quickly run out of oxygen.
Keeps Fish Healthy
Keeping fish in the dark for too long weakens their immune system, making them prone to diseases and health conditions. It also provides them with vitamin D, which all living creatures need to be healthy. Fish get it by eating plants.
Sunlight also helps some fish, including koi and goldfish, maintain their pigmentation. If they don’t get enough light, their scales fade over time, becoming lighter. Some even turn white, which is one of the most noticeable signs that fish need more light.
Helps Plants Grow
As we’ve already mentioned, plants need light for photosynthesis. Aquatic plants use both natural sunlight and aquarium lighting to synthesize food from water and carbon dioxide. Depending on the plant species in the tank, some need as much as 12 hours of light, but 8-10 is a good starting point, as we’ve explained.
Algae is also another vital element in a fish tank. While too much can cause problems, the correct levels help minimize the toxic levels of nitrogen in the water, producing oxygen and stabilizing the tank’s ecosystem.
What Kind of Light Do Fish Need?
There are multiple lights to choose from for your tank. They all offer varying levels of light, so there’s something to suit all aquariums and their inhabitants, regardless of how many fish and plants you have. Lighting is one of the most important aspects of fish ownership, so consider one of the following:
Actinic lighting emits a fluorescent blue light. It’s predominantly used as supplemental daylight light and is aesthetically pleasing when used to illuminate a tank. It’s also beneficial to photosynthesizing plants and algae.
Actinic lighting penetrates deep water better than traditional white light, making it better for large saltwater tanks. It also lights up corals and accessories inside the tank. You’ll sometimes find actinic bulbs sold as 50/50 bulbs, emitting both blue and white light.
Full-spectrum lights are also called daylight bulbs because the light they emit is similar to natural sunlight. They’re on the warm end of the spectrum and emit light from all visible wavelengths, making them excellent all-purpose bulbs for aquariums.
Color-enhancing light bulbs emit light from the warmer end of the spectrum. They’re suitable for fresh or saltwater tanks and are designed to enhance the natural coloration of fish. When looking for color-enhancing bulbs, you might see them marked up as either actinic or daylight bulbs.
Fluorescent light bulbs are some of the most commonly used in fish tanks. They’re also the most inexpensive. You can use them in both freshwater and saltwater tanks, and they work with a range of lighting systems, including standard fluorescent, compact fluorescent, T-5 HO, and VHO.
They work as a gas-discharge lamp and use electricity to excite the mercury vapors inside, producing light. The wattages vary between the bulbs and can range between 10 to 1,000 watts.
Incandescent bulbs produce light by using electricity to heat a filament wire inside. As the wire warms up, it makes a glowing light. Incandescent lights aren’t well suited to larger hobby aquariums because they produce too much heat. However, you can use them in small novelty aquariums as both a heat and light source.
Power compact bulbs are high-powered and contain around 60 lumens per watt. They’re highly versatile bulbs and a popularly used in aquarium hobby tanks. They come in three different varieties:
- Straight pin
- Square pin
- Self-ballasted screw-in
LEDs are light-emitting diodes as opposed to bulbs. They’re energy-efficient, cheap to run, and long-lasting. Hobbyists enjoy LEDs because they create a shimmering effect, which improves and enhances the tank’s appearance. They’re also beneficial if you have nocturnal inhabitants, as they emit a lunar-type light that replicates light from the moon.
Do Fish Need Natural Sunlight?
At this point, you might be asking yourself: do fish tanks need sunlight and is sunlight good for fish? Natural sunlight is the best type of light for fish, but unlike plants, fish don’t biologically need it. This means they require less if there are no plants in the tank.
However, while natural light is good for fish, direct sunlight isn’t. Most tanks need to be kept at room temperature, even throughout the night. Direct sunlight will overheat the water, causing the temperature to rise too rapidly, affecting the fish. It’ll also cause an algae bloom.
Placing the tank next to a window is a bad idea and can affect your fish’s quality of life. In the worst cases, direct sunlight leads to death. Emulating your fish’s natural conditions is the best way to keep them healthy and strong while minimizing stress.
Do Fish Like Sun or Shade?
Fish like both sun and shade. We’ve looked at the benefits of sunlight, including oxygen, vitamin D, strong immune systems, and scale coloration. However, they also need shade.
If fish are exposed to sunlight for too long (or light that’s too intense), they can get sunburnt. They also get too hot in direct sunlight, so having shady spots allows them to cool down and stay comfortable.
Even though you must provide your tank with lighting, you also need plenty of plants and accessories that fish can use for shelter and shade. That way, they can get out of the sunlight if they need to.
Do Fish Need Light To Eat?
Most fish can see in the dark, as long as there’s some light. Their retinas capture larger light frequencies, allowing them to see clearly when it’s dark. However, they see far better if the water’s clear. If it’s muddy or murky, they’ll struggle to see without the light. A fish’s eyes are made up of the following components:
- Cornea, a transparent outer layer that protects the eye from debris and damage.
- Lens, which focuses light received by the eye, forming the image.
- Iris, which adjusts the light levels and controls the amount of light that gets to the retina.
- Retina, which contains light-sensitive cells and lines the back of the eye.
Wild fish that live towards the water’s surface rely on sunlight far more readily to see their food. Even at night, there’s a little bit of light from the light reflected in the water from the moon and stars, which allows them to see food at night-time.
But fish that live in the depths of the ocean have adapted to finding food using several other organs alongside their eyes. This means they don’t need as much sunlight to be able to see.
Fish also have a lateral line, a sensory organ that helps them detect movements and changes in water pressure. This alerts them to things that are nearby, such as food and predators.
Should I Turn My Aquarium Lights off at Night?
Fish need a period of darkness to sleep. When they sleep, they stop moving and remain still to conserve their energy. They also stop reacting to stimuli.
Instead of swimming, they gently move with the currents of the water. They may correct their course with small movements of their fins, but they don’t eat or respond to light or motion unless they’re threatened. Some even bury themselves into the substrate to keep themselves still.
To do all of these things, you should provide your tank with 12 hours of darkness at night. In the wild, this indicates that night-time’s arrived. It makes them feel safer from predators and other dangers, reducing their stress levels. Turning the lights off also controls the algae growth, preventing it from getting out of control.
However, when you turn the lights off, do so gradually. Simply switching the lights off may cause them to become frightened and stressed. So, dim them as much as you can first before turning them off completely. Think about replicating the process of the sun going down as much as possible, which is what happens in the wild.
Light is one of the most essential features of your fish tank, but you must do your research to find how much sunlight your fish need. Whenever you add more plants into your tank, be sure to adjust the amount of light you provide to ensure they produce enough oxygen and vitamin D. Doing so will help your fish thrive.