I have been asked to start a thread on modern lighting techniques for reef tanks. So here we go...
I will start with discussing the various lighting technologies that are frequently used in reef tanks.
Small form factor
Little heat emitted
No need to change bulbs
Too much controllability (this will be discussed further below)
Lose efficiency after about 5 years
Can be expensive
2. T5 Fluorescent:
Many choices for bulbs and bulb combos
Need to change bulbs every 8-14 months
3. Metal Halide:
Produce a lot of heat
Need to change bulbs every 9-12 months
Consider these pros and cons when choosing a lighting technology to go with. Know that the vast majority of reef keepers are using LED lighting, although many still have success with T5 and metal halides.
Let's discuss the most important aspects of reef tank lighting. I would say that there are three main aspects of lighting that are the most important: spread, spectrum, and intensity.
I would argue that of the three, spread is the most important. You can have correct spectrum and intensity, but it is a moot point if you do not have the spread to deliver that light to the coral. This is an area where T5 and metal halide really shine (pun intended). T5 does it by being a light source that is as big as the aquarium, thus delivering light to nearly every corner of the tank. Metal halides accomplish this by using large reflectors that send the light to every corner of the tank. There are two common ways that LED light manufacturers address spread: using a wide-angle lens, or using a flat panel style light.
Wide angle lens:
The pros of the wide angle design is that it gives a natural shimmer look to the tank that many people love. This comes at a cost however. Using a point source light with a wide-angle lens creates shadows in the aquarium, thus limiting the possible areas of the tank where you can plant corals.
The pros of the panel design, is that it does a great job of limiting shadows in the aquarium, much like a T5. It does come at a cost of the shimmer, creating a much more flat look to the aquarium. Panel style lights have been much more prevalent in the hobby recently and are gaining popularity.
The spectrum of the light that is emitted is also a very important factor. The coral animal contains a symbiotic dinoflagellate called zooxanthellae that performs photosynthesis which gives energy to the coral.
This graph shows the wavelengths of light, or spectrum, that are most important for coral photosynthesis:
You will notice that most of the peaks of absorption occur within the blue spectrum. This is why most reef keepers agree that having a light that produces a wide spectral band in the 410-470 nm range is important. This is where the controllability of LEDs can be a con. It gives the user the ability to manipulate the spectrum, which can be detrimental to your corals. What looks good to the user, is not necessarily what is good for the corals. The spectrum produced by many metal halide bulbs is considered full spectrum. It is closest of all of these technologies, to the light produced by the sun. It includes wavelengths of light in the UV, far red, and IR spectrums. There is considerable debate as to the effects of these spectrums on coral growth, so I will not go into it too much.
The intensity of the light is also an important consideration. We usually measure the intensity of lighting using PAR, or Photosynthetically Active Radiation. This is measured using a PAR meter. The PAR needs of your corals depend greatly on the species of coral you are lighting. Generally, soft corals like lower light (50-100 PAR), LPS (Large Polyp Stony) like medium light (75-150 PAR), and SPS (Small Polyp Stony) like high light (200-300 PAR). These are generalizations and vary greatly depending on the specific species.
The best way to make sure that you are meeting the PAR needs of your corals is to buy or borrow a PAR meter. You can use this to tune your lights so that they are meeting the demands of your corals. Under-lighting your corals usually corresponds to lessened color and growth. You also do not want to over-light your corals, this can cause bleaching.
Popular Reef Lighting Brands:
These are some of the most popular lighting brands that have produced considerable success in many people's tanks.
Aqua Illumination Primes and Hydras
Philips Coral Care
If you decide to go with lights from any one of these manufacturers, you know that there are many people who have used these and had success, and are also willing to assist you with any questions you might have.
There are also many "budget" friendly options available. However, there is usually little information about them online, so getting help with them can be tough, which is why I generally do not recommend them to beginners. That being said, it is very possible to have great success at growing corals with budget options, such as "black box" LED fixtures from Amazon
In conclusion, there are many factors that go into mastering lighting for your reef tank. None of this matters though if you have not already gotten the hang of keeping good and stable water chemistry. Likewise, it is possible to have a great looking reef tank with sub-par lighting, if you already have good water chemistry.
Feel free to offer critiques or if you have any questions, feel free to ask them below.
*Do not quote this post so edits can be made later.