Lighting

When we talk about light, be it over a reef tank, or in the wild. We are talking about the lifeblood of the ecosystem we are trying to emulate. For many years it was considered the single most important, and 'only' requirement for corals to thrive in captivity. Today though we realise that whilst corals do retrieve a portion of their nutritional energy requirements from available light as well as actively feeding, the light portion, is still just as crucial both in its intensity, and spectrum.

In this section Ill try to cover in simple speak, both what we are trying to replicate in relation to the wild, and what it means in hard equipment and the choices we make.

Light in the wild.

In tropical climbs where our corals originate, the day night cycle is a simple 12 hours of sunlight, and 12 hours of darkness. with short intermediate transitions as the sun rises and falls quickly on the horizon compared to its slower transition as we move north or south of the equator. Due to the relatively small amount of cloud cover at these latitudes its also allot more intense for longer periods of time, and nights are typically brighter during the peak periods of the Luna cycle. In simple terms this means that your average day night cycle on a reef, consists of around 10 hours of intense illumination, 2 hours of intermediate lighting at each end, and around 10 hours 'just' short of total darkness, dependant on the moons position in the sky.

The amount of light or its intensity during the day (even with light cloud cover) is immense. To even get close to emulating its intensity, we would need to illuminate our reef tank using sunlight rated lamps with in excess of 1368 watts of light per 1msq of surface area. Even then, on a very clear sunny day, we would probably find that this still falls short of what corals are subjected to in the wild. (this is clearly visible when a beam of direct sunlight hits your tank through a window).

To further exasperate our inadequacies. Wave action causes a further intensification as each wave or ripple causes a lens effect whereby light hitting the surface is bent into a focal point resulting in a constant shimmer effect on the corals below of massively increased intensity for several meters, sometimes as much as 2 times the intensity found at the surface.. It is not currently known exactly what roll this rippling effect play's in the biology of corals but its fair to assume it does serve 'some' roll, in the way the symbiotic algae generate the food for the corals tissues from the action of photosynthesis.

The light we 'see' is a combination of differing wavelengths or 'colours' ranging from the invisible ultra violet (or UV), right through the visible blues, greens, oranges, yellows and so on, until we get to the other end, i.e. the invisible infra red. In aquatic terms (generally used by lamp and tube manufacturers) we give the 'mix' of these wavelengths an overall 'colour temperature' rated in Kelvin. Sunlight at the surface of the water generally has a colour temperature around 5000 - 6500 Kelvin, (or 'K' as it is widely known).

A graphic representation of the light spectrum

This ‘K’ rating can change dependant on the predominant mix of wavelengths. In simple terms, this means that if we increase intensity in the bluer end of the spectrum, and decrease the reds, we go UP in K rating . If we go the other way, and add more red and reduce the blues, we go DOWN in K rating. (this is important as it forms the backbone of what we look for when we choose lamps or tubes for our corals) So simply put, a blue light source, will have a higher Kelvin rating than a red one. But remember that 'Kelvin' doesn't relate to 'power'. Its simply a number derived from ambient colour temperature.

Corals and the light Spectrum....

The zooxanthellae (symbiotic algae) found in all 'near surface' photosynthesising corals, utilise light for this purpose. The offshoot of which, is glucose. This is used by the corals as an energy source for biological processes and growth. These algae are dependant on varying wavelengths of light right across the spectrum, but by and large have become adapted to slightly bluer light over millions of years of evolution due to salt waters ability to rapidly filter out more and more red light as it passes deeper and deeper. (this is what gives the ocean its darkening blue tint as we look deeper and deeper as the blue light continues to penetrate). Whilst corals do utilise differing wavelengths to differing degrees, a good portion of photosynthesis in these aquatic algae, takes part in the 420-550nm (actinic) range, which is near the blue end of the spectrum (600nm being in the 'visible' middle band, and 700nm + being at the red end ) with a second small hike in photosynthesis in the 650-700nm range. We call this range of Photo synthetically preferred light 'PAR' or more precisely 'Photo synthetically available radiation' The image below shows these peaks in activity. The scale on the left is the % of relative activity.

The main reason for this evolutionary trait as already stated is the filtering effect that salt water and any particulates present have on the light spectrum as it passes through it. When we try to emulate these conditions in the relatively shallow confines of our aquariums it should be remembered that we are not trying to recreate light as it would be seen right at the surface. We 'should' be trying to replicate the spectrum and intensity of light that the corals would receive in the 2 - 20m range. A range that most of our more commonly available corals come from.

Intensity and depth...........

As already stated, If we increase in depth, we loose more and more light, especially from the red end of the spectrum causing a bluer and bluer tint as we go down. Effectively, we see an ‘increase’ in Kelvin rating towards the bluer end of the spectrum as we go deeper and a loss of overall PAR. The degree of depletion in intensity across the ‘full’ spectrum, is quite staggering though. On the open coral reef, light intensity at 5 meters, is nearly half what it is at the surface, at 10 meters it drops by half again, and so on and so forth. To some degree, this actually works to our benefit as aquarists, in that at it becomes easier for us to emulate an average of 2-10meters natural intensity, by utilising one or more of the modern methods of creating artificial light to create these conditions in the average 0.5- 0.9m depth we use in aquarium design..

Methods of creating reef lighting.

Today, there are two main methods of replicating natural light over our reef tanks. Both have benefits and drawbacks so its up to the individual to decide which is most appropriate.

Method 1:

Tube, or ‘Fluorescent’ lighting. These come in various types, wattages, and sizes i.e. T12 and T8, Normal Output (or ‘NO’) tubes. T5 high output tubes which require electronic ballasts, or VHO which look like a T5’s but are looped back at the ends into double banks. They all have a relatively low running cost, emit less heat, and have a relatively cheap initial outlay compared to the more expensive alternatives. They do have drawbacks though. In that you need a lot of them to get anywhere near natural light levels. They also require annual replacement to prevent severe spectral drift though ageing, and distribute light in a diffused manner that looses that dappling effect mentioned earlier, that may prove to be important but requires further research.

Method 2:

Metal Halide ( or MH) lamps, come in a wide range of colour renditions ( ‘K’ ratings), come in both UV shielded single end fitment, and ‘unshielded’ double ended fitment, which should never be used without a protective UV filtering glass. For sheer outright punch, MH lamps have tubes beat hands down in most cases. Come in a variety of wattages and can punch light into the deepest of tanks. Additionally with them being a ‘point’ source of light because they use a central light producing chamber, they give that natural dappling and shimmering effect that brings a tank visually to life, and creates that much needed look of authenticity as far as replicating natural conditions for livestock.

I won’t talk much more about fluorescent tubes beyond what has already been covered, but there will be connected issues that Ill cover further on. So for now, I’ll continue on the Metal halide path, as this is usually the most logical choice where the keeping of hard or stony corals of the LPS/SPS families are concerned.

Choose your weapon of choice……

Metal halides consist of three key components.

1. The Lamp (bulb)

2. The reflector......

3. The Ballast…

The lamp is probably the single most important component of the whole setup. Depending on the depth of the tank and the types of corals kept, our choices range from 150 to 250 to 400watt or in extreme cases 1000watt versions. We can also choose from various colour or Kelvin ratings, i.e. 6500K, 10000K, 12000K, 14000K, 20000K and the oddball of the family the 50000K. In terms of longevity. Metal halides don't suffer the spectral shift of Tubes but they will see a decline in overall PAR with a 12-18month period so its best to consider replacement somewhere in the middle of this period.

The picture below represents an approximation of the visible differences between a given manufacturers lamps in relation to the overall appearance and colour dominance as viewed by the eye. Taking that into consideration, try not to look at the 'colour' in this image, more the degree of 'difference' in tone from one to the other.

The important thing to remember here is that Kelvin rating ‘as already mentioned’ is a 'representation' of the mix of wavelengths used to create that particular ‘visible’ appearance of overall colour. It is by no means a scientific standard. And it is not unusual for one manufacturer’s 10K to actually appear more like the 12K of another. As to the relevance of the 50K lamp. I’m still at a loss as far as this ones concerned, as are many others.

You’ll remember earlier that I mentioned PAR or 'Photo synthetically available radiation'. This is the figure used to show how much of the total output of any given lamp is suitable for photosynthesis which by and large, is quite near the two opposing ends of what we can visually see with the human eye. The remainder is simply there to fill the gap because our eyes require it to make things visible by bouncing these visible wavelengths of light back to our eyes. PAR value usually (with a few minor exceptions) drops with increasing Kelvin rating, because although we have increased the amount of light in the blue (420-550nm) range we have reduced the amount of light transmitted both in the middle (visible area) and at the other end (the 650nm+ range). This can easily be witnessed by the fact that a 10K lamp will 'usually' appear much brighter (and yellow'er) than its 20K equivalent, as will a 6.5K compared to its 10K relative. This is by no means a definite though, where similar rated lamps from differing manufacturers are concerned, because the K rating principle is widely open to interpretation by some manufacturers and ones idea of a 10K maybe another's idea of a 14K. Equally, total PAR, may be leaned more towards the 650+nm range than the 420+nm range or visa versa. So its a difficult call dependant what 'type' of PAR your after in relation to what depth you are trying to emulate. In effect. The total PAR of a 400W 20K may be the same as 250W 10K, but the PAR of the 20K will be peaked in the 420+nm end, whereas the PAR of the 10K may be peaked more towards a 50/50 ..... 420+nm/650+nm split.

Overall ‘general’ trends:

1. Higher Wattage = higher output and deeper penetration

2. Higher Kelvin / same wattage = Lower overall PAR and visual intensity

3. Higher Kelvin = A more blue appearance.

For reef-keepers these ‘general’ trends allow us to choose either a single or combination of colours and wattages to get the best results for us visually, whilst still providing our corals with the type of light they need. But never forget that with an increase in Kelvin, a proportional loss of PAR will usually be encountered. Which whilst not so important on shallower tanks, It may prove inadequate on larger deeper systems.

Many people 'Myself included' who keep shallower water SPS corals, get round this dilemma by utilising a combination of visually brighter lower Kelvin lamps in the 10K or 6.5K range to get the maximum intensity into the tank and keep that 650nm+ range present as it would be on the upper reef, and then back this up with the addition of extra ‘Actinic’ T5’s that give out an extra dedicated burst of light in the 420-550nm ‘Actinic’ range so essential for deeper water photosynthesis. Personally, I’ve found the use of 10K lamps backed with supplementary Actinic’s, both pleasing to the eye and adequately intense enough for even the most demanding of light requiring corals.

My reasoning for this is simple, In that if you look at any lamp, regardless of wattage, its final designed output, is dictated not only by the corals requirements, but also by our own visual needs. A single watt can only go so far, and it will always be a compromise by the manufacturer as far as wattage allocation goes across the spectrum if a lamp manufacturer has to cater for these factors in the lamps design. In effect, regardless of overall wattage, only a % of the wattage is directed into creating light in the wavelengths required for coral growth/photosynthesis, the rest is shunted into the visible range for 'our' benefit.

In practice, it’s a bit like playing with a graphic equaliser, where you can slide the buttons to boost certain acoustic wavelengths to give you more bass, treble, or midrange. If you boost the base you loose a proportional amount of allocated power to the other ranges. Your overall ‘volume’ output hasn’t changed, you’ve simply changed the ‘tone’ of the music.

This is where I feel supplemental Actinic’s come into there own, and serve a valuable purpose in reef lighting. If we look at a 150W 10K lamp, we may find that somewhere in the region of 30% of that power is allocated to the 420-550nm range (approximately 45 Watts). If we were to go to a 20K we might find nearer 50% allocated (approximately 75 watts) but the tank will look very blue and less vibrant/bright due to the losses in the visual spectrum and the losses incurred to the 'still valuable' 650nm+ range. If you want a visually bright tank that emulates the upper 2-5m of the reef, a way round this, is to go for the higher PAR of the lower K lamp (accepting it will look a more white/yellow in appearance, and then add back in more blue light to balance things out with the dedicated Actinic’s. On a 4ft 38W Actinic T5, nearly 90% will be dedicated to the 420-550nm range. So our final combination would be somewhere back in the region of 75 watts dedicated light at 420-550nm (much the same as the 20K) but with the benefit of being visually ‘bright’ to the eye and more importantly, we have retained light in the 650nm+ range where photosynthesis still takes place. If we are settling for deeper water corals i.e. those commonly found below 5 meters, then we may consider that 14K's or even 20K's on there own are adequate because these corals are used to having a reduced upper spectrum. It may be considered though, that if we 'are' going down this route, then we may wish to consider using a higher wattage lamp to keep total PAR as high as possible remembering that its still very difficult to get anywhere near intensities compared to natural light. Or we may consider a mix of lamps over differing areas of the tank, i.e. a 14-20K over lower lying rock structures, and a 10K over pinnacles etc. This can add a greater depth of field to the tank, visually stretching the difference between shallower and deeper regions.

Can I over light a tank.

Generally no as far as SPS corals are concerned. But some LPS and soft corals including some mushrooms and polyps, can suffer from bleaching if over illuminated. Because they are more commonly found below the 5 meter mark where light penetration and flow is reduced, or in sheltered Lagoonal habitats that have high sediment and particulate levels that equally reduce light penetration, they have become adapted on the whole to a more subdued and sheltered existence. In all cases it is strongly advised that if you are switching to halides from T5 lighting, or are introducing new corals, that you either raise the lights up to start with and pull back lighting periods to reduce light shock and possible UV damage, or place newer corals at the bottom of the tank for a few weeks whilst they build up protective pigments at which point they can gradually be moved up a bit at a time into more intense light.. Likewise, lighting duration shouldn't be over stretched because the active/rest patterns of some organisms especially fish can be severely disrupted leading to health problems. Some studies have been done that point towards the fact that lighting corals anywhere beyond 10-12 hours has little if any effect on improved growth rates and can cause stress related infections in more delicate species of fish such as Tangs etc..

Reflectors.

1 2

After the Lamp itself, the reflector is probably the biggest decider on how effectively your electricity is put to good use. The way a reflector bounces light that's being emitted from the lamp (or tube for that matter) down into your tank plays a major roll in how much of your energy input is converted to light that's usable for your corals and not wasted. A poorly designed reflector, will disperse light over a wider area than your tank surface (effectively lighting the surrounding floor/room ), may have hot spots in its focal range that concentrate light into odd pockets that over illuminate some areas whilst leaving others dim. and will bounce light back through the lamp which will cause it to run beyond its recommended temperature which may alter its spectral output. A correctly designed reflector will bounce light 'around' the lamp and then downwards in a relatively evenly distributed beam, or gently expanding beam, that keeps as much light focused into the tank as possible with little to no overspill.

The two images above represent today's most commonly used reflectors be they for single ended lamps with built in UV shielding, or double ended which require the addition of a UV filter glass placed directly underneath. Image 1. is the most up to date reflector of the diamond design. This is a very efficient design that reflects light in a very evenly distributed path, and catches any light emitted within a 360deg angle from the lamp. It doesn't matter whether light light is emitted from the sides, ends, or the top of the lamp. nearly all light emitted is reflected back around the lamp and downwards towards the water surface with a minimal amount of overspill.

In image 2 we see a slightly older design the Gull arm, or twin parabolic reflector. The dip in the top effectively splits light that is emitted from the upper surface of the lamp into two beams that bound back around (rather than through) the lamp and then downwards towards the water surface. although still very efficient. this design does have one drawback in that it doesn't catch light emitted from the ends of the lamp so it does loose out a little on efficiency. This twin parabolic feature is also found at the top of the diamond reflectors as well. Likewise some tube lighting manufacturers such as D&D Aquarium solutions utilise a twin parabolic design in their T5/T8 reflectors as well, to maximise potential from a given fluorescent tube..

There is always much debate as to whether a 'dimpled' or 'smooth' finish is desirable. To this date I've seen no conclusive proof in terms of coral health as to which is more preferable. The overriding factor in all cases is how reflective the material used is. In effect, a highly polished (mirror) finish be that dimpled or smooth will reflect light away from its surface without changing its spectrum or loosing intensity. A tarnished or discoloured finish may take out, or alter certain sections of the spectrum that are required for coral growth as well as lowering overall reflective efficiency. So its advised that whatever method you use, you clean your reflectors regularly to get rid of salt creep or discolouration to maintain peak efficiency.

The Ballast units..

Metal halide lamps require a ballast unit to generate the high start up ampage, and regulate the voltage to run them properly. These can be either magnetic or electronic dependant on your needs and the Lamp manufacturers recommendations. Magnetic ballasts are typically heavier than electronic ones, run hotter, and can be a little noisy on start up.

Electronic ballasts on the other hand, offer a lighter more compact design, run cooler, and offer increased energy efficiency over magnetic rivals. Some manufacturers claim as much as a 30% saving in running costs. As to how true this is is anyone's guess to be honest, but its fair to say that they 'are' more efficient. as well as giving a more stable power output which gives marginally better results from the lamp.

Whichever method you use, remember that magnetic ballasts run very hot so should never be placed anywhere that would be damaged by heat and should be well ventilated. Likewise because of the high electrical loads involved, they should be protected from water and salt spray. Likewise you will also need a 'contactor'. This is a piece of kit designed to control the start up of the lamp without burning out any timers the unit is wired to. It is strongly advised not to run high wattage lamps direct from a timer as it may burn out in the 'on' position whilst your away causing your lights to stay permanently on, until you return.

A typical 400W electronic ballast from Vue Technology

A word of caution: Cheaper 'Industrial' lighting units or MH floodlights commonly come with what's known as an MH/MV ballast ( Metal Halide/ Mercury Vapour ). These should never be used to light MH Lamps for aquarium use, as they are not efficient enough at controlling the voltage requirements of the lamps. The light emitted can vary massively in terms of spectral output with large amounts of UV combined as a consequence, which can cause severe damage to livestock etc.. Please ensure when buying ballasts that were not specifically designed for aquarium use, that they are of the MH/SO (Metal Halide/ High Pressure Sodium) variety and not MH/MV.

Which set up is right for me.?

Well that depends on whether your a cosmetically orientated person, or a functional person. You can either opt for one of the many attractive 'pendant' units that have everything combined in an attractive casing, or you can opt for separate components in kit form to mix and match each component to suite your needs and get the maximum potential. Personally, I'm a fan of separates as the all in one units, do tend to compromise a little on efficiency in favour of aesthetics' especially in the reflector department.

All in one Arcadia Pendant unit.

Separate components......(Lamp, Contactor, Ballast, Reflector, hanging kit )

Many thanks to Rob at www.marine-lighting.co.uk for the loan of the images used in this section and for his ongoing support with the new lighting set-up. I would strongly advise a look at Robs site, as he has just about anything you could need as far as tank illumination goes at fantastic prices. and a few more bits besides.