ambient room light in most instances is enough light for the fish to receive appropriate nutrients. (yes there are some exceptions we can all think about and create for sake of arguement).
tank lights are usually flourescents--not the same as the sun. the fish do not get what they need from "electrical lighting". they need at least indirect sun light. Light is typically the last issue causing problems. think about our own issues with vitamin d in the winter months--simple distance from sun in winter stops us from getting as much as we need. plenty of "sun light". just not close enough. many similarities with fish.
The lights that come with tanks are really so hobbyists can enjoy the fish. not really doing anything for the fish themselves.
tank lights are usually flourescents--not the same as the sun. the fish do not get what they need from "electrical lighting". they need at least indirect sun light. Light is typically the last issue causing problems. think about our own issues with vitamin d in the winter months--simple distance from sun in winter stops us from getting as much as we need. plenty of "sun light". just not close enough. many similarities with fish.
The lights that come with tanks are really so hobbyists can enjoy the fish. not really doing anything for the fish themselves.