The intensity of the light is another major requirement. Plants take millions of years to adapt to the light of their native surroundings. Many species of tropical plants, especially the red leaf type, are very much light lovers. Others, for example, like the species Cryptocoryne will do great in shade.
For fluorescent lights with a daylight spectrum, the rule of thumb is 1 watt for every two quarts of water. Energy efficient lamps have a higher out put. Spiral fluorescent tubes are substantially brighter than straight ones. The luminosity of lumilux tubes is about 30 % greater. For these lamps, 0.3 watts per quart of water is more than sufficient.
The deeper the light penetrates into the water, the more it diminishes. That is, the top of the tank will get more light. If your large background plants are thriving and the small ones in front are not, you should choose different types of tubes that are more luminous. You could also install another fluorescent tube. The same is true with a tank that has been prepared with peat. The brownish color of the water causes more light to be absorbed and less reaches the plants.
