This first in a series of articles on lighting is aimed at people new to the hobby who may be a little confused by all the lighting options available to illuminate a marine aquarium. Some of this may appear simplified to more experienced aquarists but, hey! We’ve all got to start somewhere! See elsewhere on the site for articles that go into lighting in greater depth.
Why light the aquarium in the first place?
The majority of the animals, the fishes and invertebrates that we keep in the reef aquarium, come from the tropics where the midday sun can be extremely bright. One adaptation to this abundant light is that many species of invertebrates, in particular the corals that we keep in our aquaria, have adapted to a way of life that involves a symbiotic relationship with single celled plants that convert sunlight into energy to the benefit of their host through the process of photosynthesis. So, to successfully maintain these animals in captivity we need to provide them with a comparatively large amount of light.
Types of lighting:
Although there are a number of different types of lighting that can be used in the hobby there are a few things that they all have in common. They all produce light and to a lesser or greater extent they all produce heat. Lamps are rated in terms of watts to give an indication of their power output and energy consumption. Additionally, lamps used for aquatics have a Kelvin rating e.g. 6500˚K, 10000˚K, 14000˚K, 20000˚K. This is a description of the colour of light the lamp produces in much the same way as domestic lights get rated as being, “warm white”, “white”, or “cool white”. This is often also referred to as the spectrum of the lamp. To an extent the choice of Kelvin rating used over a reef tank is down to the aesthetics of the aquarist – the colour that gives the effect that the aquarist finds most pleasing. Going from 6500˚K, through the intermediate ratings, and up to 20000˚K will give an effect similar to that of how colour changes with increasing depth. At the time of writing there seems to be trend to use around 14000˚K in the UK and Europe, with many aquarists in the US going for the far bluer colouration of 20000˚K. There is variation in colour between lamps of the same Kelvin rating produced by different manufacturers so the choice is somewhat subjective. Anything between 10000˚K and 14000˚K will be fine for the majority of corals you’re likely to keep as a newcomer so don’t worry about it too much.
Note: There often seems to be a perception that the bigger the Kelvin number is the more powerful the light. The Kelvin rating refers to colour, while wattage indicates power.
(For a more in depth examination of Kelvin rating and water depth, please look out for a further article on this subject)
Lamp Fitting Designation.
All the different types of lamp have some sort of designation to describe what lamp fitting each particular lamp is suited to e.g. T8, T5, RX7s etc, These fittings are standardised so a lamp designated, say RX7s (150w metal halide lamp), no matter who the manufacturer is, will fit any RX7s fitting.
Remember: Just because you have a lighting unit that’s made by a company such as Arcadia, it doesn’t mean you have to replace the lamp with an Arcadia one. Any lamp with the same type of fitting can be used in that unit.
These can be split into 2 categories, linear fluorescent lights – the familiar fluorescent tube, and PL lamps or power compacts – also sometimes referred to as energy saving bulbs.
Linear fluorescent lights can vary in length, wattage (usually proportional to the length), fitting –T12, T8, T6, T5, etc. and Kelvin rating. There are also different outputs of fluorescent available: NO (normal output), HO (high output), and VHO (very high output) but with the exception of T5 lights these are not seen often in the UK. Regarding T5 lights, beware if you’re trying to put something together on the cheap; the lights produced by reputable aquatic manufacturers will essentially be HO lights, whereas the majority of T5 lamps you see at low prices in the DIY shops are NO lamps and will produce less light. Not really recommended for aquaria deeper than 45cms (18 inches).
Multiple lamps are required to provide sufficient illumination for a reef and, to get the best out of them, they need to be close to the surface of the water. This can present problems when it comes to accessing the tank to carry out maintenance and also brings with it the potential for overheating the water if the top of the tank is enclosed.
T5 lamps usually have a greater power output than T8 lamps but have the downside of running at a higher temperature, which in turn may influence the running temperature of the aquarium.
PL lamps or compact fluorescents are in effect a linear lamp that has been either folded back on itself or looped round in perhaps a spiral. Fittings here can vary quite a bit but the most common ones for aquarium use have either 2 or 4 pins in a straight line. Watch out for cheap (inferior) imports, mostly of Chinese origin, where the lamps have the 4 pins arranged in a square – you’re unlikely to be able to find any quality lamps with a spectrum suited to aquarium usage to replace these with when they, almost inevitably, fail.
Power Compacts have the advantage of producing more light in a smaller area due to their configuration, the downside here is again heat, plus their shape means that the reflector cannot be used as efficiently so they may produce less light than a linear lamp of the same wattage.
It is possible to compensate for the lower output of fluorescent lighting by extending the photoperiod, that’s the length of time the aquarium is lit to represent a tropical day. A day length of 12 to 14 hours is acceptable.
Metal Halide (MH) Lighting.
Metal halide lighting (sometimes also referred to as HQI lighting) is currently the gold standard in reef aquarium lighting. These lights throw out a lot of light and also a lot of heat, aquariums utilising multiple MH lighting units often need the addition of a chiller to keep the water down to a temperature suitable for corals. Available in wattages ranging from 70w, through 150w, 250 w, and 400w, up to a crazy 1000w!! 70w is not much used and is a bit on the low side, 150w is very common but probably best thought of as entry level MH lighting, 250 w is a great choice for most usage, 400w is probably best employed over deeper than average tanks, and while 1000w is more the preserve of public aquarium systems, that’s not to say that hobbyists don’t go to this extreme – I know of hobbyist tanks that are lit with three 1000w MH lights!
Aquarium MH lighting units (or luminaires) are generally ugly and heavy items of equipment that need to be suspended from the ceiling above the tank. They offer light penetration to a greater depth than fluorescents and are probably better suited to maintaining corals because of the “glitter lines” they produce, emulating the same effect as the sun produces in the wild. Glitter lines are the ever-changing patterns of light and shadow you see on the base of the aquarium (much the same as you see in shallow water at the beach). You get these with MH lighting as the light is a point source the same as the sun, this effect gives the reef aquarium a far more dynamic appearance with shadows being well defined; fluorescent lighting is a diffuse light source and you’re unlikely to get glitter lines without fairly extreme surface agitation. The situation is slightly better with power compacts as they are put out more light in a smaller area than linear lamps.
Other advantages of MH lighting over fluorescents include retaining access to the aquarium for maintenance, the fact that the lights are further away from the water surrounded by air which will, to a certain extent, mitigate the problem of heat transfer.
Keep the cover glass protecting the bulb clean to optimise light output. A build up of salt from minor splashes will soon reduce the amount of light reaching the aquarium.
Don’t run lamps without a cover glass or you may end up exposing your corals to excess UV radiation, which could cause them to bleach.
Manufacturers specify a minimum distance for the light to hung above water level as a safety precaution: water splashing against the hot cover glass, perhaps at feeding time, may cause the glass to shatter
The Components of a Lighting System.
So far I’ve talked about lighting as a whole but an aspect of lighting that’s not as well appreciated as it should be is that any lighting system is the sum of 3 separate factors. Lamp, ballast, and reflector all contribute to the overall efficiency of any lighting system. If each of these elements has been optimised to work well with the other 2 then you’ll have a great lighting system, but one inferior element may mean you could be actually producing less light than a well put together lighting unit of a lower wattage. It’s quite possible to put together a single 250w MH light that will out perform an off the shelf 400w unit of inferior design.
A reflector is essential to make the most of the light emitted by your lighting system. This is mostly applicable to fluorescent lighting where the separate components are often bought separately – don’t forget to install reflectors, particularly in Juwel conversions and the like.
In the UK most aquarium lighting systems used, especially MH ones, are complete packages put together by the manufacturer. It’s worth noting that nearly all of these MH units are compromised by the small size of reflector that is used.
Keep reflectors clean to optimise light output.
The ballast is the box of tricks that makes the lamp light up. There are 2 types of ballast on the market, electromagnetic and electronic. Electromagnetic ballasts are the traditional method of lighting lamps; they tend to be heavy and waste energy in the form of heat. With fluorescent lighting, an inefficient ballast can consume almost as much electricity as the lamp itself so don’t be fooled into thinking that your 36 w lamp is only using 36w, it may be using say, another 30w, meaning your “low wattage” 36w lamp is actually using 60w or more!
Electronic ballasts are a more recent introduction; they are lightweight and far more efficient, consuming only a few extra watts of electricity, produce less heat, and extend the life of the lamp. They run much cooler than traditional ballasts. I have electronic ballasts that run at a low enough temperature that you can comfortably rest your hand on them, contrast this with electromagnetic ballasts that may run at around 120˚ Celsius, ouch!
It’s worth noting that some T5 lamps need to be run with electronic ballasts otherwise they won’t light.
There are also high-frequency electronic ballasts available that can give an increase in power output of around 10%.
Much of the above refers to fluorescent lamps, but there are also electronic ballasts available for MH lamps, which offer similar improvements in performance but the energy saving is not as marked as it is with fluorescents.
Lamps, bulbs, tubes, whatever you want to call them – different manufacturer’s lamps will perform differently when run with different ballasts. This is an area where a little experimentation may pay off to find the lamp that is best suited to your ballasts.
Lamps don’t last forever. It’s good practise to replace them when the output has reduced by 30%. A rule of thumb would be to change lamps yearly but as a number of factors influence how quickly lamps deteriorate I must stress that this figure is just give for guidance. A more accurate way of determining the life of a lamp would be to measure its output with a PAR meter. (For more on PAR and PAR meters, please look out for a further article on this subject).
Be careful handling MH lamps with bare hands as secretions from the fingertips may cause bulb failure.
Double ended MH bulbs should be fitted with the inner exhaust tip pointing upwards (the small piece of glass sticking out of the inner bulb where it was sealed at the factory).
MH lamps should be allowed to cool down for a few minutes after being turned off, before they are re-ignited.
Actinic and Dusk / Dawn Lighting.
Blue lighting is often referred to as actinic lighting; it’s been common practise to run these lamps in addition to regular lighting to bring out fluorescence in corals. This practise is probably not necessary with today’s lamps, as they should be generating plenty of light in the correct part of the spectrum to fulfil this requirement.
Where these blue coloured lamps do come in useful is as a way of producing a dusk / dawn effect by having them come on half an hour to an hour before the main lights and then going off a similar length of time after the main lights have been extinguished. This goes someway towards replicating the natural dusk / dawn effect and also prevents animals from being spooked by being suddenly exposed to something roughly equivalent to the midday sun or by being suddenly plunged into darkness at the end of the day.
Note: With all lighting it’s important to employ timers to ensure a regular photoperiod for you reef.
Above all, please remember that there’s no “best” lighting for a reef tank – only the lighting most appropriate to the animals being kept.
Any questions or comments, please feel free to get in touch with me.