Correct light in the Aquarium

1. What light does and why is that important.

Light plays an important role in the oxygen production by plants and is required by fish and other aquatic animals to function correctly. Only in the presence of light plants synthesize organic compounds from simple inorganic substances. Light regulates the basic fish life processes. Additional feature which correct lighting gives is improvement of visual presentation of the aquarium and it's inhabitants.

The amount of light that gets inside the aquarium depends on many factors: the angle of the light which hits the tank, water clarity (which influences the amount of absorbed and scattered rays of light in water), the number of obstacles encountered. Plants need mostly blue and red parts of the light.

2. Aquarium lighting depending on water depth.

Light intensity changes (decreases) with the depth (height) of the tank changes light intensity. So keep in mind that the higher the aquarium is the stronger lighting you have to install.

power light depends on the depth

3. The types of light sources used in the aquarium.


Natural light source used in addition to artificial lighting. If the sun was the only source of light then in the winter months there would be a shortage of light and plants vegetation would be slowed down. Sun light is not recommended for use. You should never place an aquarium on the windowsill as it will accelerate the algae growth and high temperature changes between night and day.

Light bulbs

This light source becomes less and less popular. Standard light bulbs become very hot (which may lead to water temperature increase) and their efficiency is not that good (only 5% of the energy is converted into light. The rest of the energy is converted into heat). Standard light bulbs emit a lot of red light.

Fluorescent light

Now widely used as an artificial source of the light. This source of light is very economical (long life, cheap to buy, about 15% of the energy is converted into light). Fluorescent light bulbs emit more blue light. They are also available in different colors. Fluorescent lighting

Now widely used as an artificial source of the light. This source of light is very economical (long life, cheap to buy, about 15% of the energy is converted into light). Fluorescent light bulbs emit more blue light. They are also available in different colors. Fluorescent lighting intensity reduces with time. The fluorescent lights life time is around one year.

Mercury lamps (HQL)

Characterized by high performance and low operating costs (as opposed to fluorescent lamps this do not lose its light intensity along the time). Recommended for use in the aquariums with height greater than 60 cm. Designed for aquarium with no cover (they should not be mounted directly above the water). You have to remember that if you use very strong light in your aquarium you need to supply carbon dioxide for plants to grow better.

Metal halide lamps (HQI)

Are more appropriate than the mercury lamps due to the better light color. Also suitable for large tanks. If used for large tanks you may need additional light source (spot light source would be useful). This lamps have short live time and become quite hot. You have to remember that if you use very strong light in your aquarium you need to supply carbon dioxide for plants to grow better.

LED Lighting

is the most expensive solution (purchase cost) but also the cheapest in terms of cost to run. Mainly used to light the aquarium at night (low light output). This light is not suitable for plants.

4. Which lighting is good for the plants.

When it comes to plant grow the best light waves for photosynthesis are 400-450nm and 650-700nm. Not to importent are light waves around 550nm. The following graph shows the dependence of photosynthesis speed throughout the light spectrum:

graph of light and photosynthesis speed in the aquarium

On the market there are many fluorescent lamps specially designed for plant growing such as: Philips Aquarelle, Osram, Sylvania Grolux, Hagen Aqua Glo, but they are not cheap. Let us examine whether it is worth investing in this type of light. Let's start from the light parameters that are the most important for aquarium.

4.1. Lighting parameters.

Fluorescent lighting is characterized by the following parameters:

  •  color rendering index (CRI or RA) maximum value of RA is 100. Sun has RA = 100. When RA is between 80 and 90 it means this light have a good color rendering, while the RA greater than 90 is a very good color rendering. RA less than 80 is very rare. Comparison of color rendering index between RA = 70-100 and RA = 30-50 is shown below. You can see how RA = 30-50 gives a bit different colours. color factor Ra
  • Color Temperature (measured in Kelvin degrees K) - White light has color temperature between 5500 to 6500K. Light which has temperature below 5500K becomes yellow or orange while if it is above 6500K gives blue light color.
  • Brightness of the light (measured in lumens lm) - it is a brightness that human eye can see. Human eye can see the best light wave of 500-600nm. The larger the amplitude of those wavelength in the spectrum of the light then human eye seems to think that this source of light is brighter. It should be noted that if we take the comparison of two tubes, one of which will have a larger amplitude of the range 400-500nm and the other will have more 500-600nm than even if both light tubes will give the same amount of light, humen eye will think that second light tube is brighter
  • Power(measured in Watts W) - is a parameter that reflects the actual amount of light that we have in the aquarium. This parameter will help us to determine amount of watts per litter getting into our aquarium (eg. 200L aquarium with two light bulbs which each has 35W -total 70W will give 70/200 = 0.35 W / litter). The greater the power of the light then better. When you try to compare power of light you should always compare the same type of light eg. fluorescent lamps with fluorescent lamps, halogen lamps with halogens etc.

Parameter RA, brightness and color temperature are not important for the plants saying that light should have low color temperature is only a myth. The second myth is that the special aquarium lamps are better than standard fluorescent lamps. Lamps specially designed for aquarium, made by famous companies are nicely packaged and have a fantastic names but they are made using the same technology and their features are very similar to conventional fluorescent lamps. However a significant difference in price will be noticeable. It is true that fluorescent lamps are better and worse, but I want to tell you that there is no lamps not to be suitable for the aquarium. All light sources have rich spectrum and if the plants grow poorly in the aquarium. If your plants are not growing correctly look into the characteristics of water, nutrient access (provided by fish or artificial fertilizer like carbon dioxide) and lighting power in the aquarium.

5. Temperature of the fluorescent light (colour).

If you're wondering what color of the light give light sources with different light temperature then take a look at spectral diagram below.

color of light with different color temperature

Below, there are aquariums which have different light sources installed - various popular brands with different light temperatures.

2700 K
aquarium with light 2700K
3000 K
aquarium with light 3000K
4000 K
aquarium with light 4000K
5200 K
aquarium with light 5200K
6500 K
aquarium with light 6500K
8500 K
aquarium with light 8500K
10000 K
aquarium with light 10000K
15,000 K
aquarium with light 15000K
18,000 K
aquarium with light 18000K

As you can see, the color corresponds to the spectral diagram. If anyone would like to have a nice effect in the aquarium then can easily go to the store and buy a suitable fluorescent tube with desired color temperature. You can mix two different fluorescent tubes and get a mix of colors.

NOTE. Some lamps can not be used alone because they can increase the algae growth so mixing two fluorescent lamps which have different color temperatures is a good solution.

6. T5 or T8 fluorescent tubes, which to choose?

There are  T5 and T8 fluorescent tubed available on the market. Will try to explain the differences between those two types:

  • diameter is different - T8 has 26mm and T5 16mm .
  • different length - eg 24W T5 has length of 55 cm, and T8 25W has length of 74 cm.
  • T5 has a longer time life compared to T8
  • T5 is more energy-efficient
  • T5 is more expensive than T8 - depending on the manufacturer from 10% to even 130%
  • T5 requires a special electronic elements which is not cheap and increases cost of the entire system. The advantage of this electronics is energy saving and no flickering effect.

It tells us that the purchase of T5 is a good choice in terms of performance and the benefits it gives you like small size, high efficiency, long service life. However, the difference in price compared to T8 is significant. Therefore before the purchase carefully consider which one to choose. When choosing to remember that T8 light parameters are not really different from T5 tubes in terms of the spectrum of light and the rate of RA. They have a slightly lower viability and efficiency but also will bring colors of the fish in the aquarium. Both tubes T5 and T8 will keep the growth of plants.

7. Light descriptions (865, 965, 840, 930) What does it mean?

These numbers contain encoded RA factor and color temperature. Lets look at some examples: Philips 840 tells us that  RA factor is greater than 80 and less than 90 (figure 8) and the color temperature is 4000K (number 40). Another example - 965 says that RA is greater than 90 which is very good and the bulbs are more expensive than eights, a color temperature of 6500K. Sometimes there are minor differences, such as NARVA Biovital 955, which has a color temperature of 5800K rather than the 5500K which is suggested by the number 55. So, in order to accurately assess the color temperature and RA factor refer to the documentation of the fluorescent  tube or go to the manufacturer's website.

8. T8, T5 and T5 tubes with width of the T8 tubes.

The price, size, power, and spectra of individual fluorescent tubes are presented below to give you a picture of what manufacturers currently have to offer. I hope that will help you to select desired tube. This ranking is quite big so I decided to put them on separate page. Link below.

You'll find there fluorescent tubes from many manufacturers with all color temperatures. Prices are taken from online stores (average prices). The aquarium shops can be a bit more expensive. I do not want to show exactly how much they cost. The main reason is to provide the difference in price between the different tubes, so that you can determine which is the most economic.

I wish you a nice reading and analysis :).

9. Calculating correct light power.

There are different methods to estimate the required light output. The old Ringwald's rule says that 1 dm2 area of the tank bottom should have 0.75 W fluorescent lighting or 2W of standard light bulbs power (this is accurate for 30-litre tank). Another rule says that there should be 0.5W of light power per litre of water. It really all depends on the depth of the tank and on what we will keep in it. For planted aquariums lighting should be about 0.6 W / litre of water. It is important to maintain the correct balance between the power of light and the amount of nutrients available to plants. We will waste light power if we will not supply enough nutrients for plants.

The more lumens light has then the human eye thinks that the light is brighter. However, the human eye can be fooled and not always brighter light means that the number of photons emitted by it is greater. To determine the amount of light required we need to taken into account another parameter - the number of watts light have. To reduce light losses you can also use reflectors. Reflectors are made of highly polished (like a mirror) aluminum casings for fluorescent lamps which direct all light downward, maintaining the lowest possible light losses. This reduces requirement of the light output of up to 30%. They are not expensive (from $5 to $15). Result can be seen straight away after installing it in the aquarium. You should also keep the surface of water in motion otherwise it will act like a mirror reflecting the light and causing losses. To do that use filters, aerators, etc.

Note. If you have strong light in the aquarium you should provide carbon dioxide and nutrients in larger quantities for plants. However be careful not to damage the biological balance. When you excess amount of nutrients and plants will not be able to use them all algae will start to grow.

10. Lighting installation tips.

To have light in aquarium as close as possible to the natural lighting it is recommended to mix light tubes (eg, red and blue fluorescent lamps, fluorescent lamps of warm and cool light, etc). It is important that during the day tank was lighted for 12-14 hours. Light sources  should be mounted in the aquarium cover (purchased at a pet store or made by yourself). You need to insulate the interior with aluminum foil, by painting with white paint or mount mirrors inside it to reduce light losses. Fluorescent tube length should be shorter than the aquarium as you will need space for elements which will attach the light to the cover. Stronger light should be at the front of the tank (plants will buckle in the direction of the light). You should replace tubes one by one with month interval between each change