Corals rely on the sun's rays to aid the microorganisms living within the coral called zooxanthellae to photosynthesize and provide the coral nutrients to thrive. The coral and the zooxanthellae have a SYMBIOTIC relationship. This means that the coral and zooxanthellae have a mutual relationship, in which they depend on each other to survive. In other words, they complete each other in the best way possible! The zooxanthellae are housed with the coral providing the coral nutrients as it photosynthesizes from the rays of the sun. Meanwhile, the coral itself provides a home that protects the zooxanthellae from the elements and use coral waste, such as CO2 and Nitrogen, as a food source. These living zooxanthellae are the reason why corals seem to glow in the dark and provide the corals with the vibrant colors you see during the day. If lighting is not sufficient and the zooxanthellae cannot photosynthesize, the zooxanthellae will be expelled from the coral, a process known as coral bleaching, and the coral will die soon after.
Given that, aquarium lighting needs to mimic the sun rays as best as possible in order for this symbiotic relationship to continue. Over the years hobbyists have tried many different ways to replicate the natural lighting conditions of the ocean and have come far enough to have generally agreed on (3) different lighting systems. We will walk you through the three different types of lighting that have been most successful in keeping corals happy, but in the end it will be up to you to choose which is the best fit for your aesthetic needs. The three most common lighting systems are as follows in chronologically developed order:
Fluorescent (T5, PC, VHO) bulbs have been used by hobbyists for the longest period of time. These types of lighting used to be used to to sustain a reef tank on its own but nowadays people use these as a addition or supplement to their more powerful lighting sources that will be discussed below. The benefit of fluorescent lights lie within the fact that they have a wide spectrum that tends to highlight the colors of the coral in a way metal halide does not. Many hobbyists combine a white bulb in addition to a blue bulb to provide a full spectrum to highlight all different aspects of their aquarium. Others combine these fluorescents with more intense metal halide lighting, that may drown out some of the colors, in order to give the coral colors more of an accent. The downside to these lights is that fluorescent bulbs tend to burn out or shift color fairly quickly and must be replaced every 6-8 months.
Metal Halide (MH, HQI) lights are very intense and powerful, in which they give corals and other inhabitants more than enough light with just one bulb. As these lights are white and extremely powerful, the corals in the tank will radiate and shimmer. Although these lights do not have a wide spectrum per se, some people prefer these lights as they mimic more intense daytime sunlight. One of the downsides of using metal halide lights is that they tend to run extremely hot and may significantly increase the temperature of the water in your tank. Many people need to pair these lights with a chiller during the summer season or find a way for proper ventilation. Another downside is that the bulb itself may cost over $100 and require replacement every year or so. These bulbs come either as single ended bulbs or double ended bulbs. The "double ended" bulbs actually produce higher than wanted UV rays due to not having a UV shield, in which may be damaging to your inhabitants. Be sure to have glass between the light and the water before using the double ended bulbs.
Light Emitting Diodes (LED) are the newest addition to aquarium lighting systems that have people curious on just what they are and why its becoming increasingly popular. These LED lighting systems have a few notable upsides, one of which is that they can emit a significant amount of light with very little energy consumption. How you may ask? These bulbs are not illuminated by a filament like ordinary incandescent bulbs but are actually illuminated by the movement of electrons in a semi-conductor material. By utilizing this energy efficient new technology, a 70W LED unit can emit as much light as a 250W metal halide and keep cool doing it! The LEDs remain relatively cool even when it's been running for long periods of time. Additionally, these LED lights should last someone a lifetime without ever changing it out! LEDs come in all sorts of colors that smoothly cascade between each other, giving you full control of the range of colors. There are LED units that even change color based on lunar information that comes from the internet, giving corals a very natural simulation of the day and night. A major downside to this technology is that they can be very pricey. On top of that the light emitted from the LEDs are narrow and does not have a wide spread to cover a lot of bigger tanks. People sometimes needs multiple units to make sure their whole tank is lit or they purchase special lenses that widen the emission of light. Lastly, people are still in debate whether these lights realistically simulate sunlight whereby coral can be grown. As for us, we have not heard too many negative things about coral propagation with LEDs and we personally have not had any issues with coral not thriving in LED lit environments.
All in all, all of those lighting systems have their merits and each one can be used to make your tank look amazing. We would suggest checking each of these out at your local fish store to see just how different or similar they are at lighting up various aquariums. Like we said earlier, it all comes down to personal preference and aesthetic taste. Isn't it nice to have options?