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Types and proper lighting for plants grown in aquariums

Ludwigia helminthorrhiza Myriophyllum spicatum Anubias afzelii Hygrophila Polysperma Nymphaea pubescens Anubias gracilis Lilaeopsis brasiliensis

Brief Description

One of the biggest debates that have been going on for years is “what is the correct lighting for my planted tank”. Basically there is no easy answer to this question. It is a proven fact that fish are a lot happier in a planted tank, their coloration will stand out more and they will feel a lot more secure than if they were being kept in an unplanted tank so getting the plants to grow successfully is well worth while.


So lets take one step backwards from the original question and ask why plants need the lighting in the first place. Plants grow by a process called photosynthesis, this is a complicated process in itself so let me try to explain how it works.

Photosynthesis is the process where plants need to convert carbon dioxide gas and water into cell building glucose and oxygen. In nature the equation for this is:-

6CO2 + 6H2O + sunlight = C6H12O6 + 6O2

Looking at the equation it may still seem baffling but quite simply it means that in daylight the plants soak up the CO2 produced by the fish respiration plus water to convert it into oxygen and glucose that will give the plant energy for growth. When nighttime falls it is reversed as the plants will then absorb oxygen and release CO2.This is one of the main reasons in an aquarium that keepers of planted tanks will turn off their CO2 systems at night to prevent excess CO2 removing oxygen from the water, this obviously would not be good for fish and plants alike.

In an aquarium there is not a chance of introducing enough sunlight to allow the photosynthesis to occur, therefore artificial sunlight has to be added, this is done by using aquarium lighting.

Strong light is normally recommended for plant growth but to make matters even more complicated there are three basic groups of plants that require different lighting levels. When you buy aquarium plants information on how much lighting is need for each type of plant should be given i.e. low lighting, medium lighting, and high lighting.

With non-planted tanks the lighting units supplied with an aquarium is perfectly adequate for the keeper as they are just looking for a lighting system that shows off the colours of their fish in the best possible way, when we start introducing plants stronger lighting units are often required. To be fair to aquarium manufacturers, a lot of them are now recognizing the demand for better lighting systems and will include them as standard in the more modern set ups.

Most keepers of planted tanks agree that the general rule for lighting is 2-3 watts per gallon (4.55 litre, 1.20 US gallon).

Tubes, bulbs etc. are often rated in their wattage when you buy them but there are other ratings that should be taken into account when you decide on which lighting system is best for your tank.


The tubes or bulbs that you buy will have various wattage ratings depending on which size you buy, this particularly applies in tubes as the greater the wattage the longer the tube will be. An 18 watt tube is normally 60 cm (23.62 inch) in length whereas a 54 watt tube will be 121-122 cm (~48 inch) in length and so on.

The wattage is the amount of electrical power that the light will use. Different lighting systems can produce varying amounts of light for the same wattage, generally the more well known makes will produce better quality lighting for a slightly costlier price.

Remember though that if your lighting unit uses four 54 watt tubes then the amount of power being used will be 4 x 54 watts which will work out to 216 watts of electrical power. Running costs on the more powerful units will be more than with the smaller units.


Lumens is basically the amount of light that the bulb or tube will produce, this information used to be quite clearly marked on the packaging supplied but nowadays it is not so easy to find when you buy your lighting. A light that has a high lumen rating will appear very bright to the human eye, the only problem with this is that our eyes pick up light in the green spectrum more than any other colour spectrum. Plants need light that is strong in the red and blue spectrum, therefore powerful lumen ratings will probably mean that the tank looks well illuminated but the plants do not benefit.

Kelvin Rating

This defines the colour spectrum that the bulb or tube is strongest in. Many of the marine lighting units will have a high kelvin rating as the corals and macro algae need a lot of blue light for growth, in freshwater set ups the plants need more light from the red band so the kelvin rating will be lower as the concentration on the spectrum shifts from the blue to the red.

Initially aquariums were supplied with incandescent bulbs that were o.k. for viewing the fish but not a lot else. As times moved on fluorescent lighting took over the market, this then started giving the aquarium owner a lot more choice as to which type of lighting they wished to use. Daylight tubes were introduced for strong, bright lighting, plant grow tubes for planted aquariums, and actinic etc. for marine tanks.

The next step was to bring out units that produced more light in the same sized units. T8 light tubes are the same length as standard tubes but produce a lot more light, this then led to the T5 tubes which produce a lot more light than the T8’s.

These light units are alright for use in tanks that are of a standard depth, some of the more modern tank designs are deeper, because of this a few keepers of planted tanks are now starting to use suspended metal halide units over the tanks, these produce light that will reach a much greater depth.

The main things to remember when deciding which lighting to use are that the lighting needs to be of the right colour spectrum for plant growth. A really bright light may not be beneficial to the plants if there is not enough light from the red spectrum reaching them. I would always use tubes that have a kelvin rating below 10,000K, marine tubes will be sold at 20,000K for the blue spectrum.

When deciding which unit to use, take into account the depth of the tank as well as the length.

The length of time that the lighting is supplied to the aquarium is a critical point as well. Most keepers of planted aquariums will run their lighting systems for 10-12 hours per day. This is not a fixed rule for a couple or reasons, every aquarium will have different needs, what works in one tank may be detrimental to another.

Leaving you lighting on for long periods may encourage a lot of algal growth, this is not what you want to see in a well looked after tank.

Plants also need nutrients adding to the water for growth.

Nutrients + Light = Algae

There are a couple of ways of stopping the algal growth, the obvious one being reduce the amount of unused nutrients being added to the water. Two other ways of dealing with this problem is to reduce the period that the lighting is switched on for, an hour less can have a big impact on the algal growth or lack of it. Another old trick is to turn the lights off for an hour midway through the day; this will interrupt the cycle of the algal growth and eventually should prevent any algae appearing at all.

As mentioned earlier different plants have different lighting requirements, research the plants that you wish to add and try to get plants that have the same needs. Why invest in a powerful light unit when your plants have low lighting needs. A quick search on the internet should provide you with the information you need but as a rough guide the following should help:-

If you do find that the lighting is too powerful for some of the plants that you have then try adding some floating plants like Salvinia to block out some of the light, another way is to plant in the shadow of other plants.

Let’s now look at some of the lighting units that are available or were widely used in the past:-

Incandescent lighting:-

Incandescent lighting is the forerunner to all of the modern units now available. In the early days of fish keeping this was the only choice, in its day it was considered to be great when the tank was illuminated and the livestock was being shown off. Economically it was poor; the power needed to create the lighting was high compared to the newer units and the bulbs created a great deal of heat which in turn increased the evaporation of the water in the tank. One of my first tanks many moons ago was supplied with a 15 watt bulb (it was only an 11 gallon (~50 litres, 13 US gallons) tank) and to my amazement the Java ferns and Amazon swords flourished under it. It was only later when I researched that I realized these were low lighting plants anyway. The colour given off by these bulbs was always a bit distorted as the Kelvin rating was very low.

Halogen bulbs are more often used nowadays for the smaller set ups. This was a step in the right direction but they are still inefficient with the power usage. The light given off is brighter but still not a true colouration that is given by other types of lighting.

Fluorescent lighting:-

Fluorescent lighting was one of the big innovations of aquarium lighting, power wise it runs a lot more efficiently than incandescent lighting and a full range of different wattage and Kelvin rated tubes are available to buy. This meant that the choice of plants available to grow successfully in a planted tank increased dramatically. Most of the original fluorescent units consisted of two tubes that were powered by separate ballast, often this ballast needed cooling by a fan due to excessive heat being produced whilst in operation.

The next step for this lighting was to slim down the tubes to give the same amount of light but for less wattage, this brought down the running costs and also meant that in some units four tubes could be included. The new tubes were known as T8’s and these were closely followed by the T5’s, now the choice of plants was endless. The new slimmer tubes were run by electronic ballast, in the more modern units this was built in making them a much better choice.

Metal Halide Lighting:-

With some of the deeper tanks Metal Halide lighting is the only way to get the light down to the bottom of the tank for the foreground planting. The units are usually suspended over the aquarium on wires and are very powerful indeed. These are not cheap to run; some units are using 800 watt bulbs. The advantage of these is that with them being suspended over the tank, the water will cause shadows to run through the tank landscape with a rippling effect just like sunlight does in nature.

Whatever type of lighting you decide to use, there are a couple of things to take note of.

Bulbs or tubes will lose their effectiveness over a period of time; they will need replacing after 6-9 months to keep your light unit efficient.

If you purchase a complete tank set up the unit that it comes with may not be adequate for a planted tank, check to see if you need to upgrade.

Do not overdo the lighting, if the unit is too powerful it can scorch the plants and kill them off, particularly with floating plants.

Lighting units run on electricity, if a unit is faulty replace it immediately; water and electric do not mix.

Feel free to visit Aquarium Lighting at too!

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