Basic Lighting options for the Reef Tank
When keeping light loving Photosynthetic corals (coral that obtains nourishment from its symbiotic algae known as Zooxanthellae) one of the most essential components of a reef set up are light units that supply light of the correct quality and quantity.
In this basic guide I will endeavour to introduce the most popular current lighting systems and lamp temperatures available to the would be reef keeper.
T8 Fluorescent lighting
These tubes are commonly known as standard/normal output tubes and are 1 inch in diameter. Although once popular they are now considered inferior technology if used as the only means of lighting. Although they are quite cheap to purchase this usually turns out to be false economy for the reasons below. These tubes are often used to supplement Metal Halides with Actinic lighting(very blue tubes high in UV that give a deep sea look and can produce fluorescence in corals).
1. The tubes are quite bulky
2. They usually have to be mounted inside a hood
3. Their output is relatively low
4. Between 6 to 8 tubes have to be used to achieve required intensity, as the tubes are quite bulky installation of this many tubes can be difficult
5. Relatively short useable life span of around 8 months before intensity and/or spectrum shifts.
6. Intensity can be poor in tanks deeper than 18 inches.
Typical T8 Tube
T5 Fluorescent lighting
This is the modern high output replacement to the T8 tube. It's thinner at 5/8 of an inch making installation easier and luminaire options are available so can be hung above or attached to the aquarium rim. The majority of corals can be maintained under these tubes in tanks up to 24 inches deep. Fewer tubes are needed due to their higher output and have longer working lives than T8’s typically lasting 12 months or more before intensity drops or spectrum shifts. Certain lamp manufacturers quote these lamps of having a life of 15000 hours.They are also run on electronic ballasts so dont create as much heat as T8 magnetic ballasts plus the ballasts are lighter and smaller than their T8 equivalents.
1. Lack punch for tanks over 24” deep
2. Heat can be problematic when using 4 or more tubes in an enclosed installation.
3. Can be expensive to replace all at once if using a number of tubes
4. Quite fragile and easily broken when handling
Typical T5 tubes
Metal Halide lamps
These lamps are considered the reef lighting of choice by the majority of reef keepers at the time of writing. They are gas discharge lamps and as such give a point source of light unlike fluorescent tubes. This means that the lamps give a very realistic look to the aquarium with similar glitter lines sparkling through the water that you would find on a natural reef .
With lamps available up to 1000 watts extremely intense lighting can be achieved, although 150,250 and 400 watt lamps are the norm.
The lamps can be mounted in either a pre build pendant or custom fitted with the use of reflectors and external ballasts. In both instances Metal halides are usually hung above the tank on wires or built into tall custom hoods. Depending on the chosen wattage these lamps are capable of punching down into tanks that are well over 24 inches deep. Each lamp can light an area of around 2.5-3 square feet depending on the height the lamp is mounted from the water surface, wattage and reflector choice.
All of the photosynthetic corals available to the hobbyist can be maintained under these lamps depending on the wattage chosen and the application.
If custom fitting industrial low bay units care must be taken to ensure that they are running metal halide or sodium vapour ballasts. If Metal halide lamps are run on Mercury vapour ballasts excess U.V light will be emitted and kill delicate corals.Double ended Halide lamps should also never be run without cover glasses as unlike single ended lamps they carry no U.V protection built in.
Its also worth mentioning that if you wish to run Metal Halides through an external domestic timer you must run the Halide through a Contactor unit as the draw from the initial strike of the Halide with cause a Domestic timer to to melt and stick on.
A simple guide for choosing the correct Metal halide fixture for your tank is as follows:
Tanks between 0 > 24 inches deep with soft corals, LPS ,certain clams and anemones that are from deeper waters and SPS high in the tank = 150 watt halides
Tanks between 0 >36 inches deep with soft corals, LPS, SPS, anemones and clams = 250 or 400 watt halides.
1 The units can be heavy and need mounting securely
2 Halides can create a great deal of heat and necessary equipment such as fans or chillers should be installed to offset this on warm days.
3 Can be expensive to run if using the higher wattage units
4 Replacement lamps can be expensive although you may only have to replace two lamps compared with a number of T5 tubes that would be needed to achieve equal intensity.
Metal Halide Pendant
Metal Halide Custom fit reflector
Metal Halide remote Ballast
When choosing your aquarium lighting you will notice that tubes and lamps will be designated a Kelvin rating. This rating relates to the spectrum of light that will be emitted by the tube/lamp.
The colour temperature of sunlight on a sunny day at the water surface is about 6500 Kelvin. As the light penetrates through the water certain colour wavelengths get filtered out. Red ,yellow’s and greens get filtered out first in that order eventually leaving blue and violet to punch down to greater depths as these have the shortest wavelengths. The further the light travels through the water the bluer it will appear and will have a greater Kelvin value.
The most popular lamp colours for reef keeping are in the 10-14k Kelvin range as these temperatures replicate light on a shallow reef . Excellent growth can be achieved by using 6500K lamps but they tend to look yellow and unnatural needing supplementing with actinic tubes.
It should be noted though that higher Kelvin lamps such as 20k lamps generally lack the intensity of 6500-14000K lamps as they are biased towards the blue wavelength. With this in mind they are often best used in conjunction with lower Kelvin (6500-10000K) lamps to maintain intensity or PAR (photosynthetically available radiation) but also retain the ‘blue reef’ look.It is worth mentioning that one manufacturers 14k lamp may look like anothers 10k lamp so its always best to view various lamps in the flesh before making your purchase.
Typical Spectral output of a 14000K Metal Halide Lamp