Lighting For the Freshwater Aquarium

Lighting is essential for any aquarium. Plants breathe by converting sunlight and carbon dioxide into energy and oxygen – a process called photosynthesis. In order to recreate ideal lighting conditions for any aquarium, it is necessary to determine suitable lights, carbon dioxide and nutrients. For a primarily fish based tank, basic lighting is sufficient. Their lighting needs are less than that of plants to happily survive.

Conversely a plant focused tank must be specific to the environment to which your chosen plants are naturally used to. It is best to work out a completed vision to avoid unnecessary adjustments and lack of growth.


Types of Lighting

Below are the most common types of aquarium lights.

  • T8 Fluorescent Tube: This can be used for fish and plants at a very cheap cost. 25mm Diameter
  • T5 Fluorescent Tube: is smaller and more energy efficient than a T8. They emit more power from a smaller 16mm diameter tube.
  • Metal Halide: High intensity light great for plants and deeper aquariums.
  • HPS: High intensity light also great for strong plant growth and deep aquariums.
  • LED:  More expensive to buy but cheaper to run generating little heat and great for fish and plants.


How much light is enough?

For a tank full of fish, with little to no plants, it is better to use a lower amount of light. In the wild , certain species like shaded areas and with no places to hide, too much light will cause them undue stress. A rule of thumb is about ½ a watt per litre of water. Eg. A 200 litre tank should have at least 100 watts of light. Your fish can survive on less so even if you don’t have ½ a watt a litre your tank will be fine. For a lush vibrant plant tank, 1 watt per litre is optimal. Bear in mind you can get to a point where there is too much light on your tank. In this case your aquarium will end up looking green and clouded due to an extremely fast growing algae bloom.

Lights should be on for at least 8 – 14 hours a day depending on the type of lights you own. Anything longer and you will be adding extra stress to your fish, algae to your tank or just unnecessarily wasting electricity. Anything less and plants will not gain sufficient light to grow. This will also add undue stress to your fish, as they need a certain amount of light for reproduction and growth.

Brighter more intense lights like metal halide & HPS Lamps will need to be on for less, otherwise more water changes will be needed to rid your tank from any excess build up of algae. Less intense lights like fluorescent tubes will need to be on for longer as the light they emit isn’t as strong and your plant life will need more. Every setup is different and to achieve the optimum result you are looking for, some of your own testing is advisable. With more light & nutrients, will come more water changes to help keep algae to a minimum.

It is best to set up your aquarium so you have your lights on for 10 – 12 hours a day. You may need to buy new lights, adjust the height of your lights or add some shading between your light and aquarium. This is to reduce the amount of light to fit into the time frame above. Some may write that lighting for your fish should be the same as their original habitat, but if you are setting up a planted aquarium and not interested in breeding fish then a little less will be ok to achieve a balance in your aquarium.

Plants need a certain amount of light in order to grow. Fish require consistency of lighting and duration. This minimizes stress and maximizes down time. Fish & Plants need time to “sleep” just as we do. Where possible, fading lights are ideal rather than sudden switch offs. The same can be said for nocturnal fish.


Plant Growth

Plants need certain spectrum’s of light and intensity to achieve strong lush growth. Aquarium bulbs will deliver the correct spectrum & intensity needed to achieve this. They will differ from brand to brand. Many aquarist’s, once they find a bulb they like, will continue purchasing it as it will best suit their needs. See Plant Care for more about plants.



In the visible spectrum of light, plants will absorb mostly the blue and red spectrum’s from the sun, thus leaving the leaves looking green. It is best to get a bulb that produces a spectrum of light similar to this. Although this is optimal for your plants, it may not be as pleasing to the your eyes. With too much of the blue and red spectrum being produced from your bulbs, a more purple tint will be given off, making your tank and room uncomfortable to be around. Fish on the other hand do not need these spectrum’s and you can use a more balanced bulb incorporating more yellow into the equation. This will result in a more naturally looking light and be a lot more pleasing to look at. If using fluorescent tubes, it is best to mix them up to give a balanced look, eliminating the unpleasing colour. This will make your aquarium more enjoyable to look at. Most aquarium bulbs will have a combination of all three as manufacturers are aware of this.

Spectrum’s from 5200K – 12000k are optimal for plant growth. This is the spectrum that plants do the best for growth. Most brands will let you know what spectrum their bulb is. This will help you in determining the best choice for your aquarium. Fish can be viewed in lower or higher spectrum’s, each spectrum will bring out a different look to your fish & plants. It may not be much but it will be noticeable.



Lux is the measure of intensity of the bulb. This will help produce strong healthy plant growth. It is best to buy a bulb with as much intensity as possible for your aquarium plants. Bulbs will weaken over time and will have to be replaced.

Guide for replacing bulbs:

Fluorescent tubes 6 – 12 months.

Metal Halide Lamps: 1 – 2 years

HPS Lamps: 2 – 3 years

LED: 3 – 4 years

It’s a good idea to change your bulbs when they start to deteriorate. Your eyes will not notice this as easily as your plants will. Pay close attention to your plants and if they are not growing as they used to, its time for new bulbs.


Bear in mind the information provided is a general overview of lighting for your aquarium. Any extra information you may need, feel free to contact us at Serene Aquarium as we look forward to hearing from you, whether query, feedback or to share your own personal experience.