Aquarium lighting plays a large part in fish health and well being. Light allows the fish to produce important vitamins like Vitamin D, while at the same time allowing plants in your aquarium to thrive and produce nutrients for the fish. However, aquarium light has to be regulated, as too much or too little can be detrimental to aquarium health.
Research your Fish
Determine how long you should leave your light on by studying the types of fish you have. Certain fish have certain needs, and those needs may be determined by the amount of light that they receive. All fish require times devoted to light and darkness, however. There are no fish, and also no aquariums, that thrive on constant sunlight, and none that thrive on constant darkness.
Set a Timer
Most of the time, after researching your fish, you will find out that almost all fish require between six and 12 hours of light in a 24-hour period. If the fish require six hours of light, have one cycle per day: six hours of light in the morning and 18 hours of light at night (these times depend on the amount of time you need to have your light on for your specific types of fish). Don't change your cycle once you've started it. As soon as you've hit a routine, it can be detrimental to your fish's health to change the times that you turn the light on and off during the day. Therefore, it is best to set a timer. Set the timer to the proper times and leave it. For your benefit, and for your fish, have the cycle start about an hour before you get home from work, and turn it off after you've had your enjoyment out of it and are going to bed.
Also, fish only feed while it's light out, and will usually have two feedings a day. This means that you can feed them when you get home, and then before you retire for the night. Space out the fish feedings, and keep the schedule consistent.
Other things that may affect the lighting of the tank are algae and plant life. If you have plant life that you would like to see grow and thrive in your aquarium, it may be necessary to turn your light on for a longer period of time. Like fish research, you must also do plant research for the specific types of plants you have in your tank. However, as most plants require very little light to survive, it is likely that you won't need to add more time onto your lighting schedule.
You may have to lower the time that the tank is lit because of algae growth. There are many factors to algae growth, such as the type of fish, how often and thoroughly you clean the tank (a clean tank actually makes algae grow faster, oddly enough), and most relevant, how much light the tank receives. Since algae photosynthesises, it needs light to flourish, and the more light it has, the more it blooms. If your tank is having an algae problem, and other solutions aren't working, then you may want to slowly decrease the amount of light per day in your tank. Don't do it suddenly, as fish need strict schedules--do it in small increments over time (decrease the time by five minutes every day, for instance). Don't take more than an hour away from the fish's schedule though. If the problem still persists, seek other solutions to eliminate the algae.