I stole this from Northstar24, hope it helps!
A Quick and Dirty introduction to Reef Lighting
Disclaimer: I am merely trying to put everything I learned researching the different types of reef lighting in an attempt to cut down on the ‘How much lighting to I need’ and ‘Can I use these cheap Chinese LED’s for my SPS reef tank’ threads
First, why do we need such an expensive light fixture over our reef tanks? The answer lies here:
http://saltaquarium.about.com/od/lig...eef-Lights.htm
Basically, corals are like plants, they get their energy from light. In order for this to happen, the light needs to be in the right ‘color’ or specturm. Not only does it need to reside in the right spectrum, but whatever is providing it must penetrate through the water in our tank to get to our corals (it is harder for light to penetrate water then say air)
Types of Lighting:
There are currently three main types of lighting for a reef tank. Metal Halide, T5 Fluorescent, and LED
Metal Halide
These are used primarily by old school hobbyists or those with very large or very deep tanks, as you get more coverage both from a spatial standpoint and a depth penetration stand point. Metal Halide lighting has been used for quite a while in this hobby, and there are a plethora of fixtures and bulbs available. Bulb colors range from 5K (very yellow/white) all the way up to 20K + (very blue).
It should be noted that there are two main drawbacks to this type of lighting:
Bulb replacement/cost: At least once a year these bulbs must be replaced, and depending on the brand of bulb you use, you are looking at anywhere from $50-$100 per bulb
Energy Consumption - Metal Halides will use far more energy both T5’s and LED’s
T5 Fluorescent Lighting
T5 Fluorescent lighting uses bulbs very similar to the ones you see in offfices and workshops. Please note: the bulbs and fixtures used in offices and workshops WILL NOT WORK for our tanks.
T5 lighting can be used on its own, or in conjunction with metal halide lighting. In fact, there are many commercially available lighting fixtures that use both metal halide bulbs and T5 bulbs
T5 bulbs work basically the same way as metal halide as far as spectrum goes. There are various ‘Daylight’ bulbs that are white, and various ‘actinic’ bulbs that are blue. It is the actinic bulbs or the bluer color that causes the colors in coral to ‘pop’. There are also some purple bulbs that are used to increase coral coloration
T5 bulbs need to be replaced every 6-9 months once they have reached the point of ‘phase shift’ where the light put out shifts into the red spectrum. This shift will encourage the growth of nuisance algae.
T5 lighting is more efficient than Metal halide lighting energy wise, but less efficient than LED. A rough approximation of watts needed is 3-5, and a quality fixture will have an individual reflector for each bulb in the fixture
There are also T8 and T12 fixtures that were used in the past. Generally speaking, these fixtures are not capable of supporting corals long term, and are best left to the history books. Bulb choices will be limited, and the fixtures themselves will use quite a bit of power
LED Lighting
LED lighting is the ‘new frontier’ of reef lighting, and it will be the lighting choice of the future once the cost of the fixtures come down. LED fixtures obviously use LED’s to generate light.
There are two main led fixture types, those that use 1 Watt LED’s and those that use 3 Watt LED’s. Fixtures using 1 Watt LED’s are primarily used in smaller, shallower tanks (we’ll say less than 20 inches for the sake of this beginner primer). In any tank deeper than 18 inches, I would only consider fixtures that run 3 Watt LED’s
Again, much like metal halides and T5’s the LED fixtures will have a combination of white and blue LED’s - some of the higher end fixtures have also started incorporating other colors such as violet, green, cyan, red, and orange.
If you are electrically inclined, there are may sites that offer do it yourself kits that will allow you to create a fixture of your own that is cheaper than buying a commercially available fixture
As far as the magic wattage question goes, there is no simple answer, it really depends on ones setup for LED’s. When I started my tank up, I had a combination Metal Halide / T5 fixture that was rated at 1000 watts. I replaced that with 225 watts of 3 Watt LED’s and I cannot run them more than 50% - so I basically replaced 1000 Watts halides and T5’s with ~112 watts of LED. There are also no bulbs to replace, most commercially available LED’s are rated at 50,000 hours of life
