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Post by: Essabee on October 13, 2008, 09:32:59 PM Part I – The bare essentials

This is not another high brow discussion of PAR, PUR, Lumen, LUX, Kelvin, but a practical path through the forest of technicality. The cheapest cost efficient lights available to us today are the florescent lights. The standard florescent light of yesteryear was the tri-phosphor, 1.5 inch diameter (T-12) 4feet long 40 watt strip lights which has been improved upon and we have today the thinner versions of the original some of them have been twisted to fit into very compact space (CFL). The standard tri-phosphor of yesteryear too has undergone change and we are now blessed with several choices of colours. The ballast too of the lights have undergone changes and the more efficient quick start electronic ballast are now available which can deal with a vast range of voltage fluctuation and still manage to produce efficient light through their connected bulbs.

A normal hobbyist will light a planted aquarium for only two purposes, to see the tank and provide light for the plants to grow. If we wish to see the aquarium in its true colour the light provided must have all the hues of the rainbow in the proportion that the end result is white. Such light are called full spectrum lights and the hobbyist need not look beyond such bulbs except for the intensity of the light required. Don’t you get confused by the several discussions of Kelvin colours and/or that photosynthesis needs the red and blue spectrum. Yes the plant’s chlorophyll uses these parts of the spectrum mainly but I have yet to come across any scientific work which shows (intensities being sufficient) that plants grow under any special coloured lights more than they do under full spectrum lights. 

 That being the case the need for the pricy plant special aquarium lights disappears and the hobbyist should pay their attention to the intensity required for their aquarium. Most slow growing aquatic plants have acquired the ability to grow under shaded conditions. These so called “low-light plants” grow quite well under non-shaded conditions too, that is under high lights. Then there are some plants that do not grow well without strong lights. The hobbyist must therefore decide on the intensities of light to provide to cater to the plants they intend growing.

Now we shall talk about the intensities of light required for a planted aquarium and to keep things simple we shall stick to the energy consumption of the florescent bulb which is given in Watts, assuming here that the conversion of the energy into light is a constant (which within small variations is actually the case). Next as aquariums come in varying sizes, and as we shall be speaking in terms of “Watt per Gallon” the size of aquarium to which we base our formulae shall be 50G tanks or larger (depth not more than 2 feet), and I will tell you how to relate it to smaller tanks at the end of this part.

To grow plants which have adapted themselves to being shaded you will need about 1 – 2 Watts of florescent light per gallon of tank water in your aquarium. So for a 50G tank the sum total of Watts of light you need shall be between 50 and 100. Now this light could be provided by a single bulb or several bulbs. For example you might be using 5 X 11 watt CFL or a single 55 watt bulb, the choice is yours.

For plants with moderate light requirement you would need 2 – 3 Watts of light per gallon of tank water. This would mean that you need between 100 – 150 watts of light for your 50Gallon tank. The hobbyist should always remember lights not only grow plants but also grow algae. The tank requires to be well planted with plants (moderately dense planting) to curb algae breakouts.

Tanks lighted above 3 Watts per gallon are high lit tanks and require CO2 to boost plant growth and curb algae. The management of high lit tanks is intensive and should be left to more serious hobbyist who will devote more time to their aquariums.

Now as promised I will tell you how I calculate light intensity requirements for smaller tanks. I compare the smaller tank to a 50G tank and find out how much smaller it is in percentage and add half that percentage in the require lights. For example a 10G tank is 50-10= 40 gallons smaller; that means 40/50X 100= 80% smaller; so I should add 80/2 = 40% more light. So if I want to add minimum of 1Watt per gallon light to a 10G tank I would need 40% more so my answer is 14 Watts of light.

Part II – The non-essentials

I have dealt with the bare essentials and you need not read further to own a competent planted tank lighted with fluorescents. Those hobbyists who want more from their planted tank look for some effects with the shade (tint) of colour of their lights must move away from the full spectrum bulbs only to bulbs with lopsided spectrums. First we take up those pricy aquarium plant bulbs and even before we deal with them lets look at the activity of the plant’s chlorophyll.

We find that the peak absorption is between the wavelengths 410 – 453 in one end of the spectrum and between 642 -662 on the other end of the spectrum. When you compare these wavelengths to the visible spectrum below we find that these match with the blue and the red spectrum.

That is exactly why those pricy aquarium florescent lights have a bluish-red coloured out put and make your aquarium look unnatural and do not bring out the true colour of your fish. If you look at the spectrum of these bulbs here they are:-





Now compare these with the full spectrum fluorescent we were speaking off in Part I

Looking at those spectral graphs of absorption by chlorophyll, and the peaked blues and reds of the aquarium special plant bulbs you would tend to believe that they do have an advantage over the full spectrum bulbs. That is not the case as plants do have some more tricks up their sleeves (leaves??). The trick that the plants uses are pigments which absorbs certain other parts of the spectrum and transfer the energy for photosynthesis (An advantage as algae don’t have this trick). Here look at this graph:-

So it boils down to the fact that going for other than full spectrum bulbs is not essential for as long as we have enough intensity we will have proper plant growth. Then again do we have to limit ourselves to the bland white light without any option to give some hint of colour to it? The answer is a definite NO.

I love a hint of gold in the light of the aquariums, sunlight has it naturally, and we can do it with fluorescent bulbs too. Out of the many types of fluorescent bulbs available in the market we can get those in the range of 2700K, 3000K, 3500K, 4000K, 6500K, 8000K, 8650K then again we get some coloured fluorescent bulbs for decorative purposes, I have seen reds, blues, and greens. By judicial mixing of different coloured bulbs we can create any tint in the aquarium light, and if we keep an eye on their individual spectrums we can do so without greatly compromising the plant growth.

Here I must point out that speaking in the same breath – fluorescent and Kelvin – is an anomaly as the colour spectrum of a florescent bulb does not at all match the Kelvin rated colour spectrums. Fluorescents produce bands of colour depending on the phosphors used, and the Kelvin rating of fluorescents are done by a system called “Correlated Color Temperature (CCT)”. Can you believe that by this CCT the Kelvin rating of the Grolux spectrum given above would be around 7500K although the colour is nowhere near the white you would expect! 

My personal favorite is mixing one decorative blue bulb with two bulbs of 2700K and adding another bulb in the range of 6500K, all bulbs being of the same wattage. The aquarium gets a look of being lit by a golden sun, and the plants do wonderfully well, and the differences in plant (& fish) colours are brought out so vividly.

I am incorporating here some of the spectrum of common florescent bulbs so that you can play at mixing your own brand of light.

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