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Dark Lord Owner
2,235 Posts
Discussion Starter · #1 ·
Here's is another great article from my friend George Farmer ( who is a great inspiration on our hobby, he's created tons of aquascapes and is a master.. in my opionoin. This is posted on, and by no way am i taking credit for this as this is george booths article. i think it's a great article and would love to share this with new and old hobbiests..


I've written this is an attempt to answer some of the more commonly asked questions about lighting. It is based on my own experiences and knowledge that I have gained over the last couple of years from reading magazines, books and of course the internet. Some of the content may not be 100% accurate, for this I apologise. Lighting is probably the most complex part of planted aquaria. I have tried to keep this article fairly short, easy to understand and thus helpful to all levels of fish/plantkeeper.

Lighting is THE most important aspect to a planted tank. Plants need light to photosynthesise, to survive and grow. Many potential planted aquarists fall at this first hurdle. It is not surprising though as very few tank "kits" are supplied with sufficient lighting to grow all but the lowest of light demanding species. Unfortunately many of us have to DIY to boost our levels to grow plants successfully, longterm.

Light Levels

Light measurement is a complicated subject so I will just explain the basics.

In a regular style aquarium i.e. rectangular with a depth of 24" or less, lit with fluorescent tubes and reflectors, the Watts per Gallon rule can be used to good effect. Note - This applies to tanks of more than about 20 US Gallons, less than this and generally more light is required. Watts per Gallon (WPG) is calculated simply by adding the total wattage of the tubes and dividing by the tank volume in US Gallons i.e. a 50 Gallon tank with 100W light gives 2 WPG. It is only a rough guide and does not allow for the many differences in quality, spectral output etc. of the many manufactured tubes available. It is also worth noting than in larger aquariums i.e. over 70 US G the WPG rule is more leanient.

The following increments are widely used to describe lighting levels;

0 to 1 WPG - Very Low
1 to 2 WPG - Low to Medium
2 to 3 WPG - Medium to Medium High
3 to 4 WPG or above- Medium High to High
Over 4 WPG - High to Very High

Plant Light Requirements

Different plant species require different light levels. Generally one can tell the light requirement of a plant by looking at its leaf colour. Darker green plants normally require less light as it indicates that the plant has lots of chlorophyll making it more efficient at photosynthesising. Lighter green or red plants have less chlorophyll making the plant less efficient at photosynthesising therefore requiring more light. One should use these differences in light requirements when planning the overall layout i.e. "lower light" plants should be shaded by the "higher light" plants. Examples of plant species that grow in the very low to low lighting bracket include Anubias, Cryptocoryne, Java fern and various mosses. This said most of these will still benefit from more light.

Types of Lighting

There are many types of lighting available to the aquarist today. The most commonly available and popular is the fluorescent tube. They are ideal for the aquarium as they are relatively efficient and cheap. I will concentrate on the T8 type (a measurement of the tube diameter in eighths of inches i.e. T8 is 1 inch), as these are the most commonly used. T5 power compact and linear tubes are becoming more popular and are generally more efficient although the diversity in spectral outputs, colour temps. is limited when compared to T8. For those with large aquariums or with more spare cash then Metal Halides are a good choice. The provide high intensity light but one major drawback is their inefficiency through heat.

Full-Spectrum (Tri-Phosphor) Lamps

Widely regarded as the best light for growing aquarium plants is the full-spectrum lamp. This means that the light output peaks in three (regular T8s peak in two) colours giving a "fuller" light more likely to meet the plant's photosynthesising requirements. Photosynthesis occurs most efficiently with peaks in the red and (and a lesser extent) blue parts of the spectrum. Most full-spectrum lamps will give a cool white light, ideal for both plants and for viewing and will have a high Colour Rendition Index (CRI) meaning that the illuminated objects will appear in their natural colour.

Colour Temperature

This is the colour of the tube's output measured in degrees Kelvin (K). It originates from the light given off from a piece of iron when heated to thousands of degrees K. The "best" colour temperature for plant growth replicates daylight at around noon on the Earth's equator and is approx. 5500K to 6500K. This is a white light and is normally produced by full-spectrum lamps. There are other tri-phosphor lamps available which give varying colour temps ranging from 3000K to 10000K. The lower the colour temperature the redder the light, the higher the temperature the bluer. I have heard of and experienced success stories with a wide range of colour temperatures. It is really down to personal taste and availability.

Examples of Full-Spectrum Lamps Ideal for Plant Growth (that I know are available in the UK)

Dennerle - Special-Plant 3000K Warm, yellow/orange
Hagen - Life-Glo 6700K Bright, cool white
Arcadia - Freshwater Lamp 7500K Cool white/green
Zoo Med - Tropic-Sun 5500K Warm white
Zoo Med - Ultra-Sun 6500K Bright Cool white
Interpet - Triton/Triplus 8300K Bright white/purple
Interpet - Daylight Plus 6500K Cool white

Light Control Units (Ballasts)

These provide the power to the fluorescent tube(s). Two main types are sold - magnetic and electronic. Magnetic are less efficient as a lot of the power supplied is wasted in heat i.e. a 20W tube may use 80W total power (20W for the light, 60W wasted in heat). One advantage is that they are cheaper to purchase and are known to be very reliable (in particular the Arcadia ballasts). Electronic ballasts are a lot more efficient giving off virtually no heat; they are also a lot lighter (weight) but they are more expensive. Both types of units can power either single or two tubes.

The fittings to the tube end caps can either be water-resistant or waterproof.


Reflectors (also known as light-enhancers) are a simple way of increasing the light intensity and efficiency. All the light available is reflected toward the plants. It is the cheapest and easiest way of getting the most from your lighting. To retain maximum efficiency the reflectors and tubes must be cleaned regularly.

Lighting Duration (Photoperiod)

In nature plants receive around 12 hours of sunlight per day. This can simulated by having the tank illuminated for a similar period. However, some plants will thrive with a reduced photoperiod and this brings the benefits of less possible algae growth but bear in mind that plants generally do not recognise light periods of less than 4 hours. For added benefit to fish and plants the lighting can be switched on and off in stages. This is possible with multiple tubes/light controllers and two or more timers. An example is having one tube on for an hour followed by all the tubes. At the end of the photoperiod the lighting can be dimmed in a similar fashion. This is particularly less stressful for the fish as they are not subject to sudden lighting extremes.

Photoperiod Gaps and Timers

A relatively new concept in lighting is to have a gap or "siesta" in the photoperiod. Plants can apparently adapt to a small dark period whereas algae is not so adaptable. Recommended siesta periods can be from 1 hour to 4 hours with a minimum of 4 hours of lighting either side of the siesta. This is a popular method of limiting algae growth and personally of have had great success with it and still run my lighting with a 2 hour siesta, with 5 hours of lighting either side (5 on, 2 off, 5 on). I can assume that the plants recognise that there is 12 hours of light even though the tank actually illuminated for 10 hours.

Timers are a very effective and convenient method of controlling photoperiods. One can set the timer to switch off at a time most suitable to the viewer. Personally my lights switch off just before my "bed time".

A Quick Word on Lighting, CO2, Nutrients and Algae

If you wish to have a long-term successful heavily planted aquarium, full of vibrant growing plants then I would strongly recommend having a minimum of 2 WPG (preferably 3 WPG or more). However one MUST inject CO2 and fertilise regularly if these light levels are acheived. The all important balance (see my pinned Algae article) must be kept to prevent algae blooms. More light requires more CO2 (aim for a constant 25 to 30ppm) and nutrients.

I hope this may help to answer some of your queries.

1 Posts
Incandescent bulbs -- these bulbs are the cheapest and easiest aquatic light bulb you can find. These type of bulbs are usually used in smaller fishbowl lamps and come in a variety limited colors.

229 Posts
The guide needs to be updated with information on PAR values for the various lighting fixtures (NO Fluorescent, T5, HO T5, PC, LED, etc.)

2,838 Posts

Wrote the article a while ago, i just relinked it last night into the BBA thread for better understanding why you get the algae. It has links to the information you are after, i wouldn't recommend pulling the information off of charts and relinking it because several people put a lot of hard work into finding the values and updating the threads as needed. The CFL thread not so much, but the linear tube thread is well kept. When i find an LED compendium that is well developped i'll add the link to it. for now though there is too many variables with non stock led fixtures

229 Posts

I've seen some articles on that are quite useful as well....I've see you have some links to that site too. I'll have to take some time to go through your thread and the links that are there, but it does look very useful.
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