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Fish on their own require little light and those from deep waters require less. However, we want enough light to see the fish and perhaps to grow aquatic plants in our aquarium landscape. Generally, fish need about 6 hours of lighting a day; plants need up to 10 hours per day of adequate light. It is the plants that require strong lighting in order to photosynthesise and grow in the artificial environs of our aquaria. How much light depends on the plant species involved and on the density of planting. As a general rule, about 1 watt of light power per 3 litres of water is sufficient for some plants to grow (for example, Vallisneria spiralis) and others require significantly more light. A few, suitable plants grow in low light conditions and Java Fern (Microsorum pteropus), Dwarf Anubias (Anubias barteri nana) and Cryps (Cryptocoryne species) are good examples. Fittings with reflectors direct the light to where it is needed and sit on the glass or Perspex cover plate or are mounted above the aquarium away from any splash zone. Pendant lights are installed above the tank. Apart from the appearance and type of light fitting, consideration must be given to the intensity of incident light required for your aquarium.

Most lights are not submersible and safety is the first consideration with electrical fittings when working near water.

In a 55 litre, tropical tank, 20 watts of light provided by one fluorescent, "Power Glo" Enhanced Spectrum tube is adequate for beginners. With that level of lighting, Vallisneria spiralis, Ceratophylum and Cryptocoryne species will grow and Java Fern (Microsorum pteropus) and Dwarf Anubias (Anubias barteri nana) will grow in their shade, to good effect. Plant die-back can be expected with that level of lighting, however, as it is of only moderate intensity. If other plant species or a heavily planted aquarium is desired then more light will be necessary. A larger tank will require larger lights or more tubes, in proportion to the tank size.

Moderate to intense lighting is best provided by compact fluorescent lights suspended above the tank or by metal-halide (halogen) lights.

As a general rule, for low to moderate levels of lighting, allow 1 watts per 3 to 5 litres of water.

Table : a guide to lighting, calculated by watts per litre of water for a tank 33 to 45 cms deep*

1 watt per 4 litres is dim lighting

Few plants will grow but brown algae will

1 watt per 3 litres is moderate light most aquatic plants will grow well
1 watt per 2 litre is strong light for light-loving plants or lush growth
1 watt per 1 litre is intense light minimum needed for corals
EXAMPLE: Dividing the number of litres in the tank by 3 will give a guide to moderate lighting level by watts; thus for a 210 litre tank, (210 3) = 70 watts of light minimum.

* This is a rough guide and works because capacity is a factor of aquarium size and it is assumed that the tank is no deeper than 45 cms.


Which to choose, Incandescent, Fluorescent lights, Metal-halide lights or Solid-state LEDs?

Incandescent are suitable only for small aquaria and are very inefficient lights. They give off a lot of heat and are costly to run when high intensity lighting is required. They are undesirable in today's energy conscious world because they are heavy consumers of electricity.


Full spectrum or Daylight bulbs are excellent and come in a range of light emission spectra mimicking sunlight. These type bulbs are a good choice for most aquarium applications and can be used at the same time with Actinic bulbs in Salt water setups. Full spectrum and Daylight bulbs offer a natural appearance and provide a good source of light for Freshwater plants. They are heavy consumers of electricity and may be of limited use.


Fluorescent tubes are available for aquarium use and are the cheapest option and easiest to install and consume less power than globes.  Calculated the wattage needed using the above guide. The choice of types fluoro-lights available is huge, from light spectra (measured as light temperature in kelvin) that mimicking sunlight to actinic lights that stimulate photosynthesis, especially in marine set ups with reefs and coral.


Some tubes contain a mix of full spectrum and actinic phosphors and can be useful where you have a light fixture that can hold only one tube. Full spectrum and Daylight tubes are available. Select a light from 5,000 to 6,000 kelvin, since this colour temperature approximates equatorial sunlight at noon. Tubes of 6,700 kelvin look the best in an aquarium as it appears a whiter light under which aquatic plants do very well. Corals require a light temperature of 7,000 kelvin to 10,000 kelvin for good effect and excellent growth. Choose a light spectrum to your taste- warm (reddish) or cool (bluish)- and according to the needs of the plants. Hagen's "Life-Glo" 6700K; "Aqua Glo" 18000K or "Power-Glo" 18000K T8 tubes are very good for freshwater aquaria. They are all full spectrum lights but vary in the output at particular wavelengths. "Life-Glo" 6,700K tubes give a more natural looking "daylight" but plants do better under "Aqua-Glo" or "Power-Glo" 18,000K in my experience. The latter is designed for marine aquaria and for use with African Rift Valley cichlids and the enhanced spectrum, rich in blue light, green and yellow gives a less pinkish light than "Aqua-Glo" 18000K tubes.  For marine aquaria with reef and coral growth, "Coralife" 10,000K High-Intensity Purified Super Daylight" T8 tubes are an excellent choice.  They are suited for use with African Rift Valley cichlids and also for stimulating plant growth. Tanks deeper than 61 cms (24") are not suited to this type of illumination.


Fluorescent tubes become less efficient after 2,500 hours of running, with 50% of the colour spectrum being lost at the half-life of the bulb as phosphors age. They need to be replaced at that point which means that for general purposes, they must be changed about every 5 to 6 months. Compact Fluorescents have longer life and they normally need to be replaced about every 10-12 months.


GLO T5 HO Linear Fluorescent lighting systems use the 5/8" T5 tubes (or globes) and offer a new way to illuminate aquaria. "Life-Glo" 6700K T5 HO is recommended by the makers for planted aquaria; "Power-Glo" 18000K T5 HO is recommended for use with planted freshwater aquaria and marine aquaria; and "Marine-Glo" T5 HO with output in the blue actinic range is recommended for marine reef aquaria (but may not be strong enough for small-polyp hard corals). A new range of "GLO" reflectors that house 1, 2 or 4 T5 tubes are used with these T5 tubes and give good light. Tanks deeper than 61 cms (24") are not suited to this type of illumination. Visit Hagen.


Compact fluorescent lights are an alternative to ordinary fluorescent tubes, and are ideal for small aquaria and situations where space is a consideration. Many of the later models of aquarium lamps are of this type. The difference between fluorescents and compact fluorescents is in the intensity of the light. For example: a "Sun Glo" Fluorescent 24 Light of 20 watts, at 4200 kelvin, 1230 lumens (light intensity) c.f. a Power Compact 22 11/16 light, of 55 watts, 6700 kelvin, 4230 lumens (light intensity). Compact fluorescents need to be replaced about every 10-12 months as the phosphors are less efficient after that age.

Tanks deeper than 61 cms (24") are not suited to this type of illumination.


Actinic bulbs and tubes provide their spectrum in the range required for the the Photosynthetic process and health of Marine corals and Invertebrates and to a lesser extent freshwater plants. Actinic bulbs and tubes are heavy in the blue light Blue  in the 455-470 nm range and can give everything a bluish tint. They cause some pigments to fluoresce. Actinic bulbs or tubes should not be used alone but in conjunction with other full spectrum bulbs or tubes.


New low-energy using fluorescent lights are excellent lights and their use helps cut power bills and carbon emissions. There are now models on the market, for hooded reflectors, pendant reflectors and even built-in to some all-in-one aquarium designs- all available at a premium price. Cost savings at power consumption level are off-set by high outlay per unit at start up.


Metal-halide or Halogen lamps provide excellent lighting and are the preferred option for heavily planted freshwater tanks and for marine aquaria. They come in a wide range of colour temperatures ranging from 4000o to 20000o kelvin and the Actinic 03 needed by Reef tanks. Tanks deeper than 61 cms (24") are serves best with this type of illumination. They are expensive to buy and more expensive to run, which places them out of price range for most hobbyists in my home State of South Australia where power costs are high. Halogen lights are also impact heavily on carbon emissions so do not appeal for the environmentally conscious person.  However, they still set the standard for lighting in 2007, as best displayed option- what ever the cost to your pocket or to the environment.


Solid state lighting is now possible, with promise of lower power consumption.  None have been developed sufficiently to replace demand for fluorescent or halogen lighting, yet. Stockists heavily committed to sales of the fluorescent and halogen lights appear to be resisting establishing a demand here. Wait and see what happens.


Sunlight? Well, yes, that's free and available but not practical in our homes except where sky-lights conduct sunlight into rooms. Is this the way to go to illuminate fish rooms when power costs are high? Algae grows well under sunlight, so attention will need to be given to control. Of course , most people are at work or school or play during daylight hours so viewing our fish at night will require lighting, still, so the choice comes back to fluorescent lights (T8 or T5), halogen lights or solid-state LEDs, which? 


My current preferred option is to scrap the metal-halide power guzzlers and to upgrade from standard T8 fluorescents to GLO T5 HO linear fluorescent lights.  I am currently running a twin (2 x 24 watt) GLO T5 HO "Power-Glo" 18000K light on a shallow tank (76 cm x 45 cm x 35 cm deep) and find the light bright and a bit bluer than daylight and it makes all the T8 tubes look dull in comparison! The fish look good and their colours show well. Time will tell if the plants do well under it.

Lighting Summary Chart

 Bulb Type Watts


Pros Cons Typical Use
  Incandescent 7-25 2-4
with colour
of bulb
multiple colours
lower light
high heat
Small fish only
15-40 6-18
months, depending

on the ballast

Wide range of
colours, sizes;
efficient; cool;
Functional but not ideal for
plants or
Fresh or saltwater
aquarium or mini reef or
micro reef with
low light corals and plants
  T5 HO Linear
24-54 16-24
18,000 K;
high intensity;
small size; cool
Not ideally
suited for
more than 61 cms
(24") deep

Reef less than 61 cms (24") deep

75-165 4-18
10,000 K;
Large selection
of sizes; longer
bulb life than
Higher heat- may over-heat some tanks
deep; freshwater

Reefs less than 61 cms (24") deep

10-130 12-28
high intensity;
wide spectrum
May produce
higher heat -
may heat some tanks
Reefs less 61 cms (24") deep; freshwater
planted; marine
20,000 K
intensity; wide
Higher heat
- may over-heat some tanks; possible
UV radiation
Reefs or freshwater
aquariums more
61 cms (24") deep;
corals and
  LED Moon/
  Lunar Light
1 watt
N/A (Not
a light bulb,
but a
N/A Low wattage;
great for
one unit per
every 24" of
Reef or freshwater

decorative function only

LED Bright Light  ?? LED types

solid state

?? ?? ?? the next generation


Basic information only has been given above.  Consult your stockist for advice.  Be clear about your aims (whether you wish to keep fish only, fish and some plants or mainly plants and a few fish). Be clear about your price range and ask for the best value for money.

Remember, once the lights are running, there will be power bills to pay so keep that in mind as part of your budget planning for keeping fish and plants.




kelvin: (the abbreviation is K; the term degrees is not used and the word 'kelvin' is always in lowercase unless beginning a sentence) is a colour-index that is derived by comparing the light emitted from a standard, hot, black body (a Carbon instrument). Kelvin is also a unit of temperature. As the black body is heated it glows and emits light. The amount of light produced  at each wavelength by an object depends on the temperature of the object producing the light so that solid objects at 1,000 kelvin (1,000 K) appear red but are putting out far more (invisible) infrared light. At 3,000 K a black body emits a very orange-red light, similar to the colour of a standard household tungsten filament bulb. The photosphere of the Sun radiates light at 5778 K which we call the visible, white light. At 9,000 K a black body emits a spectrum that appears very blue-white light. Interestingly, stars have their spectra measured in kelvin, too. Stars hotter than the sun (over 6,000 K) put out most of their light in the blue and ultraviolet regions of the spectrum. Stars cooler than the Sun (below 5.000 K) put out most of their light in the red and infrared regions of the spectrum. The colour spectrum refers to the content of the emitted light across all the visible light wavelengths. Many light sources are full spectrum but the amount of light at each wave length varies according to type.


actinic: adj. relating to or exhibiting actinism; relating to the chemically active rays of the electromagnetic spectrum;


actinism: noun, the intrinsic property in radiation that produces photochemical activity (actinism). Blue light in the 455-470 nm range (depending on model) that stimulates bio-fluorescence (a form of actinism) and is known as actinic light. Stimulating actinism in corals is an essential part of their growth requirements.

Fluoro tubes carry code number so what does F40T12CW/IS or F30T8 RS mean?

The F stands for fluorescent.
The next number indicates the wattage.
The T number represents the Tube diameter in eights of an inch. (T12 = 12/8ths = 1 1/4 inches, T8 = 8/8ths =1 inch, T5 = 5/8ths= 16mm.).
The letters deal with specific characteristics of the lamp, in the examples-

   CW = Cool-White and relates to the colour output of the lamp

   IS = Instant-Start and relates to the type of ballast system it is designed to be used

   RS = Rapid-Start another type of ballast system

   BS = another type of ballast system.

   HO means High Output.

   VHO means Very High Output.


spectrum (n., pl. spectra), the range of wavelengths of light emitted by a light-emitting body; the sun's visible spectrum is seen as a rainbow. For visible light, the longest wavelengths are red and the shortest, violet- given by the familiar mnemonic R O Y G B I V (red, orange, yellow, green, blue, indigo, violet). We see the combined solar spectrum as "white" light.  Artificial lights have their own spectra, with some emitting more or less at any particular wavelength. For example, sodium vapour lights emit in the yellow wavelength; mercury vapour lights emit a lot in the blue wavelengths and each fluorescent tube emits according to the phosphors that it contains. Some fluorescent lights emit the full range of wavelengths found in daylight but at different intensities at each wavelength.  A good brand will show the spectrum for its light  on the packaging and indicate the roles for which it is suited.


phosphors are light emitting chemicals that are coated on the inside of fluorescent tubes to radiate light when stimulated by Ultra-violet light. Actinic 03 is the name of one type of phosphor.



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