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Marine Tank Lighting:

 

This topic covers all the aspects of lighting, including but not limited to colour, intensity and duration.

Firstly, for fish, the amount, type and duration of lighting is not too crucial.
Lighting basically makes the fish look more attractive, and most of them will be out swimming, looking for food.

For most of the corals that we keep however, lighting is a VERY important part of their lives.
There are 2 major groups of corals, the photosynthetic and the non-photosynthetic groups.
Lighting is important for the photosynthetic group only. The other group can do with, or without it.

In the photosynthetic group, corals usually come from areas of the ocean between 5 feet to about 60 feet or so.
These could be a mixture of hard corals, soft corals, and even anemones which are a class of their own.
Whichever type, all of them have in common a type of algae called symbiotic dinoflagellates,
or zooxanthellae that live just under the coral surface.
These zooxanthellae are brown in colour, and utilise the light, as well as CO2 in order to product sugars for the corals.
It is this special type of "brown algae" that gives many light-loving corals their brown colours.
This is why many NON-photosynthetic corals like the carnations (dendronepthya, scleronepthya, etc.)
are so brilliantly coloured in pink, purple, orange, scarlet, etc., since they don't have these algal cells in their tissues.

 

Colour

Colour is quite an important part to consider. In shallow waters, sunlight is quite complete.
As you go deeper and deeper, you will lose red first, followed by orange, yellow, green, blue,
and finally purple at super depths where everything is black.
But at depths of even 60 feet, you will still have most of the colours except red and orange.
Many people (especially LFS owners) will try to tell you that actinic blue lights are critical for the success of photosynthetic corals.
This is NOT true. Actinic blue or 03 lighting is a single frequency light that peaks at 420nm, and appears purple blue.
Certain corals found deeper than 60 feet have learnt to utilise this frequency of light since they have no choice.
However, none of the corals we buy come from these depths. They come from very shallow waters where they depend on
and need full spectrum white light. The actinic blue tubes actually serve to enhance the colours of the corals (and fish).

Colour is measured in terms of colour temperature, denoted by the K (Kelvin) rating.
Noon sunlight (above water) is about 5800K, which is slightly yellow.
As the K rating goes down, the colour becomes more yellow, then orange, then red.
This is why if you look at a household fluorescent tube like Philips 827 (2700K) tubes,
the output is very yellow, the 840 (4000K) is less yellow, and the 865 (6500K) is very white with just very little yellow left.
If you go up to 10000K, the lighting will be totally white, no yellow at all, at
depending on the brand of light, you might even see a very little bit of blue.

From 10,000K onwards, The higher the K rating, the bluer the light will appear.
12000K or 14000K are considered as white-blue, and look quite good. 20,000K bulbs are blue-white,
and usually not white enough, unless you increase the power rating of the bulb used.
50,000K available nowadays are totally blue, and are only used to supplement 6500K daylight bulbs.

As far as corals are concerned, they do best and grow fastest under 6500K since this is full-spectrum.
As far as humans are concerned however, this is too yellow for the human eye, so people either add a few actinic blue tubes
to balance out the yellowness of the 6500K, or they use 10,000K or even 12,000K with or without additional actinic blue tubes.

High K-rating tubes have 4 disadvantages :

a) Lower intensity than daylight tubes, even at the same power consumption.

b) Very much higher cost

c) Very quick drop in colour from blue to white to yellow, as fast as 6 months (low colour retention)

d) Appear dimmer than daylight bulbs - because human eyes are not sensitive to blue,
and usually the way the manufacturers make the K rating higher is to reduce the
phosphors used to produce the other colours, so that more blue phosphors remain.

With these disadvantages, you might want to think twice before using 10000K, 12000K, 14000K or 20000K tubes.
10,000K isn't too bad, since it's still quite white, but within 9 months or so, it will started turning more and more yellow.

The 6500K and 6000K tubes in the market, being at natural daylight colours do not suffer a colour degradation that fast,
being able to retain their colour for as long as 1.5 - 2 years.

 

Duration

Keep your lighting on for between 8 - 12 hours. Your corals need to rest as well, and so do your fish.
Also, if you extend the period, you might start getting unwanted algae problems.
You can use a timer to control this period. It does not have to coincide with our daylight hours.
You can do say, On at 1pm, off at midnight for 11 hours. This way, after work/classes, you still get to enjoy the tank.
If you suffer a power failure, some timers need to be reset unless they have a built-in battery supply or memory feature.

 

Intensity

When we talk about intensity, generally we're not referring to Watts
- this is a measurement of power consumption, and not output.

An obvious example is a 40W incandescent light bulb compared to a 40W fluorescent (FL) tube.
The tube is VERY much brighter. Similarly, a 36W PL-L 6500K tube is also much more intense than a 36W FL tube.

The intensity of a bulb is directly related to the depth of water the light can penetrate.
For instance, a 400W MH (metal halide) bulb puts out about the same intensity as 10 X 40W FL tubes.
However, because MH light is a point-source light, ALL the intensity is concentrated at one point
and this is why it can penetrate down to at least 30" easily, whereas 40W FLs only go down to about 12" effectively.

Adding 10 FLs does NOT make any difference. You just get a much wider spread,
but the penetration is still 12" per tube, just over a wider area only.

In the past, a favourite form of measurement used to be watts/US gallon, and ranged from 5-10 W/G of white light for reef tanks.
Because reef tanks could be very odd-sized, some tall, some short, this wasn't very practical,
and nowadays more people are starting to use W/sq.ft. of surface area,
lying between 50 - 150W / sq.ft. of white light, depending on the corals you plan to keep.

Note on effective water penetration power of bulbs and tubes :
Fluorescents - down to 12"
CF like PL-L, T4 and T5 - to 15"
MH 70W to 16"
MH 150W to 20"
MH 250W to 24"
MH 400W to 30"

There are also 1000W and 2000W bulbs, but generally not for household tanks.

How intense for different types of corals : All soft corals (excluding mushrooms) do very well under medium to high intensity.
Hard corals are usually divided into LPS (large-polyp scleractinians) or SPS (small-polyped scleractinians).
LPS corals include brains, anchors, hammers, bubbles, torch, elegance, goniopora,
alveopora, plates, galaxy, etc., i.e., those where the fleshy part is very obvious and quite large.

SPS corals are those with very small polyps like Acropora, Montipora, Porites, etc. LPS corals (and mushrooms)
do fine with low to medium intensity light.
SPS do well only under high and very high intensity.

BTW, anemones also prefer high to very high intensity, depending on the species.

 

CASE STUDY : For a soft corals, I'd want to target for at least 70W/sq.ft., so in my tank,
I'll go for about 4 pieces of 36W daylight PL-L tubes, with 1 more 36W actinic blue PL-L tube for added colour.
This will be 144W of white light, and 36W of actinic blue. Bear in mind that the PL-L tubes are about 1.5" wide each,
so 5 of them will occupy at least 2/3 of the tank width already.
You still need to use AC fans to cool the tank down, especially with these many lights.

For LPS corals and mushrooms, I could use 3 pieces of 36W white PL-Ls, and a single 36W actinic blue PL-L.
For SPS corals or anemones, I would just use a single 150W 10000K or even a 250W 20000K MH.
The reason why I can use a 250W in such a shallow tank is because 20000K bulbs are very much dimmer than a 6500K anyway.

NOTE :
Whenever you're using high intensity lighting, you have to be careful not to "sunburn" your corals.
This can happen very easily, if the LFS where you bought your corals from use only FLs (like me).
If you subject these newly bought corals to intense MH light just a few inches above your coral, usually your coral will bleach.
They may even die. This is because the coral will eject their zooxanthellae since there's suddenly a lighting overload
and they don't need so much zooxanthellae anymore.
But sometimes they may get carried away.

This is the reason why LFS who do not know about lighting principles always say that you can't use MH, they'll kill your corals, etc., etc.
They just haven't acclimatised the corals yet. What you should do is to place the new arrivals at the dimmest spot first,
then week by week, move them slowly up to their final "resting place".

Just FYI, our tropical sun at noon is more than 3X brighter than a 400W MH bulb,
so you can't say that the MH will kill your corals.

 

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