The process of lighting a saltwater aquarium serves two purposes:
⪼ 1. Allow us to view the marine life and highlight the amazing colours that lie within.
⪼ 2. Mimic natural sunlight as closely as possible; to give our marine life some sort of day/night rhythm and provide food for the photosynthesising organisms such as corals, plants, coralline algae, phytoplankton and other invertebrates which use light as their energy source through photosynthesis. Ultimately this means they turn light and carbon dioxide into food (carbon), oxygen and water. The light requirement for this process is between 350- 750nm and is partly UVA.
To adequately light your marine aquarium the only 3 parameters you must consider are quality, quantity and duration of light.
Regular 12-16 hour lighting periods are optimal for good marine life health. It’s best to use timers and have the actinic bulbs only on for 1-2 hours each end to simulate dawn and dusk.
The best lighting system will be a combination of actinic (blue) and daylight bulbs.
As a general rule of thumb the bulbs needed to sustain photosynthetic light should have a color temperature of around 6500°K – 12000°K for general reef applications (color temperature increases with depth so much deeper water species require higher color temperatures, these are very specialist).
You should also aim for 3 (soft corals) to 5 (hard corals) watts of light per gallon of saltwater as another general rule, this will help you decide how many bulbs at what wattage you will need.
Optimal lighting is a delicate arrangement that is dictated by the type of saltwater aquarium you plan to keep and what creatures you plan to keep in it.
Photosynthesizing marine life falls into 3 different catergories:
⪼ 1. Low light species such as large polyped stony corals (LPS)
⪼ 2. Moderate light species such as many soft corals
⪼ 3. High light loving including many small polyped stony corals (SPS) and Tridacnid clams.
The trick here is to try and get compatible species that thrive under similar light conditions or get very creative at placing high light species higher up towards the lights and moderate light species lower in the aquarium this way you wont saturate some species with too much light (damaging) or cause some species to not receive enough lighting for good growth.
Species that are not getting as much light as they should be can to some degree be compensated with supplementary feeding such as plankton.
The most simplistic lighting requirements can be used for fish only aquariums where all you want to do is be able to view your fish and give them a day/night cycle. Fluorescent lights of normal/standard output (NO) are all that is required here; full spectrum bulbs produce a more natural looking light and actinic blue lights bring out colourful pigments nicely.
Fish Only with Live Rock (FOWLR) aquariums typically include the photosynthesizing coralline algae encrusting the live rock and a handful of select invertebrates, depending on how many and which type of corals and/or photosynthetic anemones you have you may want to go up to high output fluorescents (greater luminosity than normal output fluoros) such as a T5 set up. T5 lights have become extremely popular in the past few years. If combined with electronic ballast they run cooler, longer and more energy efficiently than other lighting set ups, they also penetrate the water better than many other types of thicker bulbs.
If you have little more than Live rock in your FOWLR simple actinic blue fluorescents will suffice to keep the photosynthetic creatures and algae happy and thus increase water quality too.
As you may have guessed by now a reef aquarium requires the most intensive lighting set up and to a reef lighting is as important for good health as filtration.
Often times lighting will be one of the most expensive components in a reef aquarium. I recommend HO fluorescents (such as T5’s) to VHO (very high output) fluorescents for deeper, larger aquariums or more sensitive species, with a combination of actinic blue and daylight bulbs.
Many aquarists use metal halide lights but because of their expense, excessive heat output, high UV radiation (use shields here), high electricity usage and limited lighting penetration over fluorescents I don’t really see the real advantage of the additional costs involved.
Retrofit systems and other fluorescent lamp housings should have the light bulbs no more than 3 inches above the water surface. Reflectors should be used to direct light to the water, many bulbs no have reflectors built in, these are very efficient.
When choosing a lighting set up you should always take into consideration:
⪼ What marine life you plan to keep
⪼ The initial cost of the system
⪼ Operating costs (electricity)
⪼ Bulb replacement costs (and frequency of replacement)
⪼ Whether or not you would need a chiller for the aquarium
⪼ The ease and eventual need for any upgrading
Some systems maybe cheaper initially but may require more frequent bulb changes or chilling systems because of heat generated making them more expensive in the long run.