Let there be light... but not too much of it. Ok... so you HAVE TO keep something in mind. MOST of the time your fish could CARE LESS about what kind of light they have up on top. Sure if it's too bright they might hide under your plants or not be able to see too well after awhile.
Generally fish need very little light and many times the little bit of light naturally occuring through the windows might even be enough for some species. Certainly in many cases the standard light fixtures are all that many fish care for. So now that we have this information covered let's move on to who the light is really for. Pick one: A) You. B) Plants/Coral. or C) Both.
It's all about you. You wanna see them fishies. SHOW ME THE COLORS!!!!
Ok... most people get their fish lit up for this reason. A big dark tank after all kind of limits what one can see. Why buy fish if you can't see them ever. So the question becomes what kind of lights do you need to do this? What makes them look better or worse under the lights?
Lights come in many types. There are incandescent, flourescent, compact flourescent, metal halide, light emitting diode (LED) and as time and technology permit... many more either there but not used currently or still yet to come. There are drawbacks for any and all formats of lights as well as great benefits.
When light is about you then you need to keep the following in mind:
Does it make the tank too hot?
Can you see your fish?
Does it make your tank look tinted a color you dont like?
Does it make your fish look bad due to the tinting or reflection of the light on the fish?
We will discuss the lighting technologies and their differences later in the article.
When you are picking lights for your preferences the technology of light you use generally does not matter much. Sure there are drawbacks and positives to many types of light but as long as you are not putting more light then your fish can be comfortable with and you are not overheating your tank and algae hasnt taken over then anything goes. This changes when you move to a planted or coral tank. When you get into this world you need to meet certain requirements for photosynthesis. There are then many more complication including fertilization, CO2 or other available carbon sources, trimming plants etc.
Plants need what is called Photo Active Radiation or PAR. This is the measurement of ultraviolet light that penetrates into the water and reaches the leaves of the plants (or coral). Depending on the height of the plant this can vary greatly. Normally lights are marked in watts and lumens. Watts is a measure of the amount of electric used and in the same type of lighting can be used to determine a brighter light. Lumens as a measurement is a better measurement in the visible light from one technology to another. It does not give you information though on which portions of the light spectrum are present. When you buy specialty lighting for aquariums this commonly is marked in degrees Kelvin. The Kelvin scale is the visible color that (do not remember if it's) hydrogen (or something else... anyone knows for sure let me know) burns at different numerical temperatures. This thus means cooler temperatures such as 4000-6000 are more yellow while those in the 9000-10000K range are more white and eventually blue.
Types of lighting that are acceptable over plants/coral? In the 1-2 gallon range you can sometimes get away with common incandescant technology lighting. After that in the 2-5 gallon range you need to use either normal flourescent strip lighting or screw in compact flourescent. Compact flourescent (CF) is also known as Power Compact or PC lighting. Compact technology is where they pretty much take a normal flourescent and fold it into a U shape straight or twist it after it's been put into a U so that there is a single ended plug. It then takes up about half the space and is commonly driven at the same or slightly higher wattage to glow brighter. These come in a large variety of lengths. Once you get into the 5-20 gallon range you can usually use CF strips as well as special multi bulb normal flourscent as well as a more recent "normal" flourescent light type called T5. T5 indicates the diameter of the light. This is representative of an approximately 1/2 inch diameter tube. Another common size is the T8 bulb.
Once you get over 20 gallons you have a large variety of fixtures and technologies depending on fans for cooling, where the lights will be mounted, the size of your tank, and more. In planted tanks you generally find somewhere between 2-5 watts per gallon of CF/PC lighting potentially coupled with T5 and finally ending up with Metal Halide (MH) fixtures when you get to the upper end of very large tanks (1000 gallon etc). Other options include High Output (HO) and Very High Output (VHO) flourescent which look like normal flourescent bulbs with special internal parts as well as high power ballasts to drive them brighter. Side effects of HO and VHO as well as large amounts of any type of bulb is heat. Without proper ventilation temperatures will rise significantly in the tank resulting in the need for cooling devices such as a chiller. Most plant tanks need something near "Normal Daylight" spectrum lighting which is in the 6500K range.
With coral tanks depending on whether you are growing hard or soft coral will tell you how many watts and the technology your tank will need based on size of tank, mounting distance for the light, and depth of tank to reach the coral. Even in smaller sized tanks with coral you generally run more then one type of light in high wattage. Heat is almost always a problem and most people running salt tanks have chillers when they run small tanks since most small tanks have tightly fitting lids on and the lights rest on top of the lid. With larger tanks the spacing of the light from the surface is usually coupled with an open top so the heat increase is limited.
Give your fish, coral, and plants what they want AND make it look "beautiful" color wise to your preferences? Sure it's possible. It depends on what you like. Some people like very yellow looking tanks. I personally don't. Your coral won't like it either. Your plants might not care so much as long as there is a lot of light. If you like more white looking tanks (8000-9000K) your coral will like you a little more and your plants will probably love you still too. When you get into the more blue spectrums of 10,000K and a specialty spectrum called 03 Actinic your coral would worship the ground you walk on if you give them enough of it. Your planted tank will likely hate you.
Of course all of the above matters only if you're giving a high wattage amount in your tank per gallon. As long as you like the colors you see AND the plants/coral get the right K range with enough watts everyone is happy.
Another factor we have not mentioned so far is the amount of time per day you light up your tank. Run it too little then there is no good results in planted/coral tanks. Run it too long and soon you have "things growing like weeds" in your aquatic garden and algae choking every inch of space it can crowd into. More on that next....
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.