Why can't I just plug it into the wall or DOH! I forgot to turn it on/off today.
Part of having success in your aquarium with fish and plants is regularity and mimicking nature when possible. If you have sufficient lighting to equal the amount of light needed during the day you can turn your lights on when the sun comes up and off at the end of the day. The issue with this is many of us have jobs that cause us to get up before the sun comes up and by the time we get home when we have a minute to sit and watch our fish the lights need to go off. If you have stronger lighting this is even further complicated by the need to have a reduced lighting period. Further complications include the fact that the sun gets brighter during the day and gradually dim which you cannot replicate with most flourescent fixtures. There is a particular brand that does allow dimming of flourescent fixtures but how efficient this is and whether it wears out the bulbs quicker or not?
Putting it simply the issue really is do you have the ability to guarantee stability in your light timing? Does the schedule end up changing on the weekends? What if you need to be away from home one night or for several days?
Introducing... the timer switch. There are many methods of controlling the lights on your fish tank. Since most of us use flourescent fixtures you need to ensure your timer is grounded. These are usually referred to as heavy duty timers where the regular "lamp" ones do not have a ground. Most of these are in the 20 amp sizing. There are mechanical, computerized, and stand-alone digital timers that operate based on gears much like a clock with "pegs" that trigger on and off settings when moved around the 24 hour dial.
The digital timers usually include a built in clock as well as a day of the week setting. These will allow you to turn a single socket on or off multiple times of the day and have a different schedule for different days of the week.
Finally the computerized timers are those programmed by a computer. These include such things as X10, INSTEON, and Control4 switches that can be setup on your computer or through special controllers. Many companies have built monitoring systems for fish tanks that include controllers for light schedules.
With these type of control systems the mechanical are usually most reliable except when power is lost. These mechanical systems require electricity to advance the dial that triggers the on and off settings. The computerized and stand-alone digital timers are more sensitive to power surges since the "little computers" inside them run on relatively low voltages. The benefit of the computerized and digital timers is that they have an internal battery backed clock. When power goes out the backup battery keeps the system "current" for the time of day. When power resumes the systems continues right where it should be having the ability to remember what it was last set to and then turn things on or off based on the next scheduled event.
The computer and digital timers sound like the best solution right? Well there are some minor drawbacks such as if the lights were on and then power went out and remained off until after the lights should have switched off. In most cases the lights will remain on because the off setting was unable to be sent to the computerized timer. Some digital stand-alone timers continue to display the current time on the screen as well as "settings" for being on/off/auto/etc. Many of those will actually continue to update the status regardless of electricity being there or not due to the backup battery keeping the status updated. When power resumes the status is current so it will result in being on or off based on the schedule.
Want to get one of these timers? Coming soon will be the final page of the lighting articles listing various products as well as nationwide vendors who sell them.