As many people know there is a common term for how much lighting you have over a planted tank called watts per gallon. This termanology should be rid of. There are several factors to look at, such as, tank length, width and height. Also physical features, like the presence of natural sunlight, color of background and sides, glass lids, shading and water displaced; there is also the actual type of light taht you are putting in to look at.
While WPG is pretty standard, it isn't exactly a good way to look at things. Watts are only a measure of how much energy is used by a bulb. Lumens are actual light output, but still wouldn't establish how effective your lights are. Beyond lumens and watts you have to look at things such as reflectors. Very few flourescent fixtures will have reflectors. As such much of your light will be lost. Another thing to look at is if you have glass lids you will have a problem with light being reflected back to the source. There is also the problem that some light will penetrate water better than others. The deeper the tank is the more light will be lost per inch, which is compounded. For the dollar the best lights to get are either high output T5 fixtures, or compact flourescent bulbs. Metal halides are very good for larger and deeper tanks, but can be very problematic for small tanks. The next thing to look at is although a tank may have 2 WPG it may not be enough for lowlights for the tank. For instance a 24" 20W bulb over a 20 H would put you at 20 wpg correct. Now the same fixture over a 20 L will have a section completely void of a light over it.
While WPG is pretty standard, it isn't exactly a good way to look at things. Watts are only a measure of how much energy is used by a bulb. Lumens are actual light output, but still wouldn't establish how effective your lights are. Beyond lumens and watts you have to look at things such as reflectors. Very few flourescent fixtures will have reflectors. As such much of your light will be lost. Another thing to look at is if you have glass lids you will have a problem with light being reflected back to the source. There is also the problem that some light will penetrate water better than others. The deeper the tank is the more light will be lost per inch, which is compounded. For the dollar the best lights to get are either high output T5 fixtures, or compact flourescent bulbs. Metal halides are very good for larger and deeper tanks, but can be very problematic for small tanks. The next thing to look at is although a tank may have 2 WPG it may not be enough for lowlights for the tank. For instance a 24" 20W bulb over a 20 H would put you at 20 wpg correct. Now the same fixture over a 20 L will have a section completely void of a light over it.
