Lighting is needed to illuminate and grow what you are displaying in your aquariums, different lights and combinations of spectrum can make coral colours become fluorescent and "pop" to create a stunning visual.
Though they don't only make your aquarium look good it is a major factor for your corals health and growth, most corals have a symbiotic algae that lives within the tissue called Zooxanthellae, it is photosynthetic therefore it uses light to produce sugars that the coral uses for energy.
In return for the nutrition that the Zooxanthellae provides, the corals stony skeleton and flesh provides a safe place for it to live.
One of the biggest decisions you will come to making is your choice in lighting, with literally hundreds of lights using various technologies the choice can be daunting.
The first factor to consider is what type of corals you're planning on keeping. Some types of coral require stronger light while others prefer less intense lighting due to the locations they are naturally found in or how adaptable they are to unfamiliar levels of light.
Your budget will also play a huge role in the selection since you can spend under $100 up to a couple of thousand dollars to illuminate the exact same system.
The price difference comes down to the brand, it's quality, programmability of the unit and wether you need optional extras to program it and of course the technology used in the unit.
Modern advances in aquarium lighting have seen the rise of LED (Light Emitting Diode) take over T5 and Metal Halide in popularity, but the former favourites are still widely used and are well proven in their capabilities to grow coral.
Metal Halide provides a great looking spectrum and a natural looking shimmer in the water, it also packs a punch with coral growth.
On the downside they draw slightly more power and produce more heat than other types of lighting such as LED.
T5 and compact fluorescent gives a very well lit appearance and using a unit with 8-10 tubes gives you plenty of options with colour spectrums.
Replacement tubes come in a nice array of colours to enhance your corals colour and still provide growth.
However replacing the tubes every 6-12 months can be a costly exercise and they do draw a decent amount of power.
The compact fluorescent tubes that are often used in off the shelf/ready to go aquariums are not very suitable for intermediate and advanced systems but they do well for most easy care corals.
LED units come in a vast array of sizes and styles, LED can provide some of the most visually stunning spectrums that make your corals fluoresce like crazy.
Some brands provide a stunning shimmer through the water and they provide great growth on most corals while using less power than T5 and metal halide units.
They do however lack in areas such as the spread of the light or the mixing of colours in some models.
The light they provide can cause some types of coral (mainly SPS corals such as Acropora) to have patchy colouration due to the lenses not spreading the light properly.
Similarly some the the units that employ a range of coloured diodes often don't properly mix the colours before they reach the coral and give a multicoloured and patchy appearance which is often unsightly in the cheaper units.
There are more types of lighting, but those are the most commonly used aquarium lights that you will encounter.
Asking advice on web forums like MAFA about lighting will open up a huge can of worms but try to soak in as much information as you can before making your decision.
T5 Lighting Fluoresent:
Not so Good-
MH Lighting Metal Hailide:
Not so Good-
LED Lighting Light Emitting Diode
Not so Good-
Information provided by:MARINE AQUARIUM FANATICS AUSTRALIA