VI. Reef Lighting - The Basics
This article discusses Fluorescent, High-Intensity Discharge & LED Lighting Options
By far the most in-depth and expensive decision you will face in starting a reef aquarium is your choice of lighting. The sheer number of manufacturers and designs can be overwhelming to the uninitiated begging a brief introductory article discussing the general options and basics of light science as it pertains to reef keeping. The ocean of lighting options becomes much easier to navigate when broken into the three primary modes of illumination utilized by each fixture, the classifications are High-Intensity Discharge, Fluorescent, L.E.D. & hybrid platforms combining any number of the three.
High-Intensity Discharge Lighting
When we speak of high-intensity discharge lighting(HID) in reef keeping we do not usually mean the horticultural or security lights many may be familiar with. These do not emit the proper spectrum of light to fuel photosynthesis in our situation and thus when we refer to HID fixtures we refer mainly to metal halide lighting. Metal halide bulbs come in two primary bulb forms; mogul base, a screw in the elongated bulb, and HQI, a double ended bulb structure, HQI is most popular and readily available in most local fish stores.
Offering color spectrums from 6500K(natural sunlight) to 20,000K(a heavily blue saturated light) and wattages from fifty to four-hundred, metal halide lights are adequate lighting for many reef applications and are especially desired for their ability to provide enough focused light to produce a natural-looking shimmer effect. These light fixtures for all their power and benefits have their own drawbacks, however, for example, the light bulbs and ballasts required to create significant heat. For really, really large tanks, the heat created by metal halide lighting is easily dispersed, however, in many situations the heat generated may be enough to make it impossible to maintain the desired temperature without the use of a chiller.
In many situations, choosing metal halide will mean more equipment, more plumbing and, more possible points of failure in our system, so, I usually refrain from metal halide lighting options except for in commercial settings where overall gallonage is high enough to offset heat dispersion and proper care can be taken to plumb a chiller with adequate failsafe protocols. Most reef aquarists are well suited to consider other options that will not add a need for system components to maintain a stable and safe operating temperature.
Fluorescent Lighting
While often overlooked in the reef hobby, fluorescent lighting, when properly maintained is a great candidate for reef lighting fixtures. When considering specifically T5HO fluorescent tubes the number of colors available in an intensity suitable for coral allows for the user to mix and match tubes of different colors on separate timers to create a desired lighting effect throughout the day. A fluorescent tube emits light in a fairly even spread across its length, albeit slightly more intense in the middle portion of the tube than on the ends. This does not, however, lead to any "spot-lighting" effect and instead, aquariums lit by T5 display a remarkably even spread of lighting across the entire tank.
When using fluorescent lighting for your reef tank it is important to remember that when sunlight is filtered by the water, the blue wavelengths are carried furthest, this means that the algae within coral have adapted to a bluer spectrum of light than the white spectrum of light we commonly see in fluorescent tubes. Most aquarium lighting manufacturers that specialize in T5HO will have tubes that fall within a blue spectrum of 420-450 nm, often labeled “Actinic”, it is important to use these actinic bulbs in conjunction with white tubes for the health of your coral.
Adequate lighting for most tanks may be provided for many tanks with T5HO fluorescents, for example; a forty gallon aquarium housing a mixture of soft leathers and large polyped stony corals, with some small polyped stony coral, kept in the top six to eight inches of the tank would do well with four to six three-foot T5 tubes. However, bulbs should be changed every four to six months to maintain the health of your small polyped stony coral and you will often not have much success with these corals deeper than six to eight inches in your tank. If you want a tank that is stocked from sand to rock crest in branching and plating stony coral, and you do not want the added hassle of chillers and ballasts associated with metal halide there is a third option to consider and in my opinion, it is the best option applied properly.
LED Lighting
When reviewing LED lighting options the hobbyist is presented with two primary formats, LED strips and LED pendants. While there are exceptions, strips primarily consist of strings of lower wattage LEDs, often one to one and a half watts per diode. Mixed colored diodes are aligned in a matrix or linear arrangement while pendants primarily consist of fewer diodes of higher wattages. Beyond the vast flexibility of options LED lighting offers superior energy efficiency and with many units, the number of settings and built-in features is worth articles of their own.
Many of these fixtures, rivaling metal halide in output at a power consumption a fraction of some fluorescent systems, also come with an initial investment above that which you would find with the other options. When we consider other factors and costs like chillers, operating expenses and bulb maintenance, the upfront investment is usually more than offset over time. LED Fixtures are sleek and often have the capability of emitting enough light to also cast a shimmering effect as seen with metal halides making them the appealing for not only energy efficiency but also aesthetic reasons.
When selecting an LED for your reef tank, leaning towards the high output pendant designs is usually best, reserving strips LED options of refugiums and freshwater planted tanks where light is at lower demand. Many of these pendants can be programmed to run standalone, or, maybe programmed with master and slave units to create complex lighting configurations that mimic natural sunrise and sunset, lightning storm effects and ambient night lighting to simulate moonlight. As many corals adapt to photoperiods and many more use it as a queue for reproductive processes, emulating a natural light scheme is advantageous in creating a conducive environment for natural coral reproduction.
Hybrid Formats
The above options each have their own strengths and weaknesses. Perhaps you are drawn to the full coverage of T5HO as you do not like the directional light provided by metal halide and LED options, or, perhaps you want the intensity of metal halides but wish to have more control over the color emitted. In these situations, different lighting systems can be used in tandem to create a balance of factors desired. Bright metal halides or heavily directional LED pendants can be used in conjunction with T5HO tubes to add a balance of light spread and give the additional option of color adjustment through the T5HO tube colors. Additionally, LEDs can be used in conjunction with T5HO or metal halide to create subtle lighting effects such as moonlighting while providing intense daily illumination.
Any number of fixtures can be used together and programmed using timers to allow for control over your lighting scheme rivaling the newer LED pendants available. There are several manufacturers that still sell all-in-one hybrid systems as well. Combining metal halide pendants with T5HO fluorescent tubes and small wattage blue LEDs for moonlighting this fixture will give you the best features of each lighting type in one package. These fixtures are more suited to larger tanks as with metal halide lighting heat can become an issue.
Because of their efficiency, life-span, the level of options and control provided and that they just plain look nice, LED lighting is by far the best option for lighting reef tanks. If you can get past the initial investment required you will be more than satisfied with your purchase. With Arduino and Raspberry Pi being used to create inventions of our own, and the cost of LED diodes and components slowly coming down, in time I see LEDs being more and more competitively priced and may one day phase out the more archaic hybrid systems previously required to provide ample and realistic lighting effects.