Lighting
for the reef aquarium can be a very confusing topic. There
are many opinions out there, some based upon hard data,
others upon personal experience. Which lighting to choose:
Normal fluorescent, Very High Output VHO fluorescent, metal
halide M/H, power compacts PC, or a combination thereof?
Before you go out and spend a lot of money on a lighting
system that may or may not be adequate for your aquarium
system, you should analyze the needs of your aquarium system.
This will, in the long run, save you lots of time, money.
DEFINITION
OF TERMS:
Color
rendering: The degree to which objects viewed under a particular
light source appear to match their true colors as seen under
daylight.
Color
temperature: The temperature, in degrees Kelvin (K) to which
a back body must be heated before it emits a light of a given
color.
VHO:
Very High Output fluorescent lighting.
NO
fluorescent: Normal fluorescent lighting
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1)
What type(s) of photosynthetic organisms do I want to keep?
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This
is a factor to consider when purchasing as lighting system.
If you are going to keep mostly soft corals and mushroom anemones,
VHO lighting, even in a deeper tank, may be sufficient (although
metal halide lighting would be preferred). If you are going
predominantly stony corals, especially SPS (small polyped
stonies) corals like _Acropora_, _Stylophora_, and the like,
metal halide is perhaps your best option, especially if you
wish to keep the intense color seen in many of these species.
Of
course, there is one last option, that being that you will
keep non-photosynthetic corals, in which case Normal fluorescent
lighting will be sufficient.
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2)
How long and wide is my tank?
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When
dealing with metal halide lighting, the number of lights you
will need depends on the length of your tank. In general,
it is safe to say that if your tank is 4' long or less, one
metal halide fixture should do. However, if your tank is longer
(6' or better) you should have at least one metal halide fixture
per two foot or three foot length (i.e. for a six foot long
tank, two metal halide fixtures should be sufficient. If the
tank is overly wide (> 2'), you may need to take that into
account, and add an additional lighting fixture or two to
compensate for the added width.
If
you opt not to use metal halide but rather prefer to go with
a fluorescent lighting source, the number of lights needed
becomes more complex as the limiting factor then becomes with
width of the tank. In order to achieve the intensity required
by some stony corals, you may need four or more VHO fluorescent
bulbs (NOrmal fluorescent bulbs are not advised except on
extremely shallow aquaria or tanks where no hermatypic corals
are to be kept).
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3)
How deep is my aquarium tank?
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This
is important to know when deciding on a lighting source. My
rule of thumb is that if the aquarium tank has a depth <16",
you might be able to get away with using a bank of VHO fluorescent.
If the aquarium tank depth is >16", metal halide should
be used to achieve light penetration to the bottom of the
tanks. A good guide to choosing the proper wattage is that
for tanks 16" or less in depth, anything from a 150 watt
to a 250 watt will be sufficient. For deeper tanks, use either
250 watt or 400 watt bulbs. From research I have done, it
has been noted that VHO fluorescent lighting does not penetrate
as far as and with the same intensity of equal wattage of
metal halide lighting. In fact, it was noted that half the
intensity of VHO fluorescent was lost within the first 12"
of depth. Using metal halide lighting of equal wattage, this
loss did not occur until 23" of depth. This is mainly
due to the fact that any fluorescent light source is considered
to be as DIFFUSE light source. Metal halide, on the other
hand, is considered a point source light. Water is a diffusing
medium, so by using an already diffuse light source over a
diffusing medium, you are further diffusing the light (i.e.
making it less intense). This situation, while it does occur
with metal halide, it not as obvious as a point source light
has greater "punching power".
This
is not to say that metal halide lighting has no place in tanks
<16" deep. Quite the contrary. It has been noted that
using metal halide, even in shallow tanks, increases coral
growth and promotes color intensity, results that are not
always seen with other lighting sources.
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4)
What type of housing should I use?
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There
are several varieties of bulb housings available to the hobbyist,
with each style providing a different area of coverage and
reflection rate. Each fixture throws off its own "cone
of light", and this needs to be taken into consideration
when choosing fixtures. Also, each shape has its own reflective
properties that are a consideration as well.
When
using metal halide, you should purchase fixtures that are
parabolic in shape if possible. This type of fixture will
direct most of the light down into the tanks. The disadvantage
to this is that they focus the light into a somewhat narrow
area. Pendant metal halide lighting is a good example of this.
There are wider curved fixtures which throw a somewhat focused
beam of light into the tank, and these work out well for the
majority of uses. Boxlike fixtures will also work providing
you can replace the (usually) flat reflective surface with
a curved one.
With
fluorescent lighting, you have little choice in the fixture
style. The shapes most commonly available appear to be adequate
to the task at hand. My only advise is to make sure the reflective
material used in fluorescent fixtures is made of polished
metal or an equivalent material.
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5)
What type(s) of bulbs should I use?
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When
using metal halide lighting, you should go for a bulb whose
kelvin rating is no less than 6500 K. LOver kelvin ratings
will provide you with a light that is very yellow, and will
throw off the color rendering a bit. You will find that you
will need to supplement this lighting with actinic 03 bulbs
to correct the spectrum. My opinion is that bulbs of 6500
K to 10,000 K are adequate for most situations. There is a
20,000 K bulb available, but is it quite blue and, as in the
case of a <6500 K bulb, the color rendering may be thrown
off. If you decide to go with a 20,000 K bulb, you may find
that you will need to supplement with one or two VHO full
spectrum bulbs to help improve the color rendering.
The
next question that comes up is if supplementation of actinic
03 radiation is needed with the higher kelvin bulbs. In my
opinion, if you are using a bulb 10,000 K or greater, supplementation
is not absolutely needed. HOWEVER, the increase in coral growth
and color provided by this supplementation makes it well worth
the additional expense. Supplementation is advisable if you
are using bulbs of 6500 K or less, and especially if you are
using lighting of 5500 K or less.
When
using fluorescent lighting, you will need to use a combination
of bulbs in order to get both as proper spectrum for the corals
and a good color rendering for you. Usually a 1:1 ration of
actinic to full spectrum should be sufficient for most purposes.
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6)
Should I use a reflector with my lights?
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The
answer to this is a resounding yes. Fortunately, most fixtures
come with a reflector already built in. You want to use a
reflector that is made of polished metal, as this will provide
the highest amount of light reflection. Many reflectors are
painted white which, while it does reflect light (not as much
as polished metal, though), tends to diffuse the light as
well and so is not as desirable as a reflective material.
If at all possible, you should place the reflector so that
it is parabolic in shape as this will provide maximum reflection.
Next best is a simple curve. The least effective is a flat
surface although it will do if no other option is available.
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7)
What about fluorescent bulbs with the built in reflectors,
or the "power twist" type bulbs. Are they really
that much more effective?
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While
both are indeed more effective, that are not that much so
and may not be worth the additional cost. In the case of a
"power twist" type bulb, you may get an increase
in intensity of 10%. This means that with a 40 watt bulb,
you will get an output equivalent to that of a 44 watt bulb.
Bulbs
with built in reflectors also provide additional intensity,
but perhaps not as much as is thought. While light is indeed
"lost" to the tank from the top of the bulb (unless
a reflector is used), it must be realized that this light,
bouncing off the reflective material, is then passed AGAIN
through the bulb. By then, there is a loss of intensity. So,
the desirability of such lights in really up to the individual
hobbyist, but in my opinion a good in-fixture reflector is
far superior to a bulb with a built in reflector
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8)
How high should my lights be above the tank?
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This
really depends on the type of light you are using. With fluorescent
lighting, you want the fixture right on the tank so that way
the maximum amount of light will reach the organisms.
With
metal halide lighting, generally speaking, 6" above the
water is sufficient. Remember that for every foot above the
tank, you will lose half the intensity. The closer, the better.
HOWEVER......if your corals are not use to the more intense
metal halide light (going from VHO to metal halide, for instance)
or if you are changing bulbs, going from a lOver kelvin rated
bulb to a higher one or just changing the bulb after 2500
hours of burn time, you may want to bring the lights up a
bit higher, perhaps 12" to 18" off the tank, to
give the organisms time to adjust to the increased UV output.
Then over a period of a few weeks (how long will depend on
how your corals react to the new lighting), lOver the lights
until they are once again 6" above the tank.
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9)
What about using UV shields on metal halide lamps? IS this
a necessity?
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In
my opinion, no it is not. Most shields will block out a good
portion, if not all, of the UV and possible the actinic 03
radiation put out by the bulb. In some corals, especially
the more colorful species, it is the UV that provides the
need for UV protective pigment production. It is these protective
pigments that provide the intense colors we see in our corals.
Without the UV, the colors tend to fade with time.
If
you decide to go sans shield, you MUST protect the bulb against
direct water contact. Water spray, such as from an air stone,
will usually not bother the bulb but a direct splash may indeed
shatter it.
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10)
How long should the photoperiod be?
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Under
normal circumstances, a photoperiod of 8 to 10.5 hours should
be sufficient. More, and you run the risk of an algae bloom
and/or stressing your corals due to an extended photoperiod.
With less, your corals may not do as well due to a lack of
sufficient photoperiod. The easiest way to do this is to place
your lights on a timer. This allows for an automatic day/night
cycle without you needing to be there. Some hobbyists have
arranged their lighting so that the actinic 03 bulbs come
on first, then the metal halide(s), this being done so as
not to "photoshock" the corals. It should be remembered
that although blue light may not appear bright to us, it IS
bright to the corals so there may be no benefit to doing this.
One
problem that faces hobbyists is that they are not home a good
portion of the day, a portion when the lights are on. To compensate
for this, they leave the lights on well past the 8 to 10.5
hours actually needed. Here again, the timers come into play.
It may be to your advantage to set the timers so that the
lights come on at 11:00 a.m. or 12:00 noon and go off at 10:00
p.m. or 11:00 p.m. This way, the corals get the light they
need, and the lights are on when you are home to enjoy the
tank.
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11)
How often should I change my bulbs?
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Generally
speaking, ANY bulb should be changed after 2500 hours of burn
time (3000 hours at most). Much after this, the intensity
decreases dramatically, and you tend to have a spectral loss
at the blue/UV end. Changing bulbs at a regular interval will
avoid this. As an example, suppose you are burning your lights
10 hours a day. Assuming 30 days per month, you would want
to change the bulbs every 8.5 months at minimum or 10 months
at maximum. One way to assure that your bulbs are changed
in a timely manner is to mark the bulbs with a felt tipped
marker with the date they were installed. This way, there
is no guessing on your part.
Also,
do NOT assume that just because a light is bright means that
it is still valuable as a reef light. This is not always the
case. Our eyes are far more sensitive to the red/yellow/orange
areas of the spectrum, while the greatest loss occurs down
at the blue/UV portion (a portion of the spectrum to which
ours eyes are not as sensitive. That's the reason high kelvin
bulbs look dimmer to us).
Over
time, as the bulbs dim, your corals become accustomed to the
lOver spectral intensity. Suddenly, as you change the bulbs,
these animals are blasted with higher levels of UV radiation
as well as visible light. This is the primary cause of "coral
burn" or coral bleaching in captive specimens. In order
to avoid this, whenever you install new lighting, or when
changing from a lOver intensity bulb to a higher intensity
bulb, you might want to raise the fixture higher over the
tank. Then over a period of a week or two, slowly lower the
fixture back to its original height. This will give the corals
time to adjust to the greater intensity. If raising the lighting
is not an option, placing a sheet of glass or UV blocking
acrylic between the bulbs and the corals should suffice.
I
hope this guide has been of some help to you. It should answer
the most commonly asked questions about lighting.
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You may also post questions to Frank Greco at our forum
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