One of the most
costly and confusing elements of your aquarium is lighting.
The “right” or “best” one is mostly determined by the animals
kept. Many different corals come
into the hobby with varying needs, i.e. Feeding,
current, medium (water chemistry), and not least of all light.
Why do corals need
light? In reality the coral
(animal) itself does not need light. However,
the zooxanthellae (algae) that live inside the tissue of the coral do need
light. The health of the algae
governs the health of the animal as the health of the animal governs the health
of the algae. This relationship is
called symbiosis.
Where a coral
commonly occurs on the reef (geographical distribution) is one of the major
governing factors as to how much and what “color” of light they are adapted
to receiving.
Intensity
Corals
occur from depths of 10 to over 300 feet of water. This depth is what governs the quality and quantity of light
that they receive. Corals that
commonly occur between 10 and 30 feet of water correspondingly require the most
intense light. Those that occur at
greater depths require less light to remain healthy.
Three types of lighting
technologies prevail in the hobby today and are used by many with
great success. The type that is “perfect” for your aquarium will be
determined mostly by your tank depth, coral community, and budget.
Power
Compacts
Power
compacts (PC) are a style of fluorescent lighting.
They are very popular with hobbyists for the ease of use and relatively
low cost. Power compacts come in
formats as small as 7 watts and as large as 96 watts. With tanks less than 24 inches deep, they can be used as the
sole light source with great success. They
are available in ready to use fixtures. They
can be unpacked , set on the tank, plugged in, and turned on.
The biggest drawback to their use is the frequent replacement of the
bulbs. Depending on the
requirements of your coral community, they could need replacement in as few as 6
months. Most hobbyists replace them
every 9 – 12 months.
Very High Output (VHO)
Very
High Output (VHO) is another type of fluorescent light.
It looks exactly the same as standard fluorescent bulbs.
But, the ballast that is used to fire them is different. VHO lighting has been popular in the hobby for quite a while.
Bulb replacement is every 9 – 12 months.
Many hobbyists prefer the ability of the VHO format to promote
fluorescing in their corals. Fluorescing
is a corals ability to produce pigments that make the light more usable by their
algae. The drawback to VHO for most
hobbyists is the assembly. They
typically do not come prewired. Although
the wiring is very basic,
it can be intimidating for those unfamiliar with the procedure.
VHO is also appropriate as the sole light source for tanks 24” deep or less.
High
Intensity Discharge
High
Intensity Discharge is referred to as Metal Halide (MH) or HQI.
MH lighting technology is different than the previous two, in that it is
a point source of light. PC and VHO are emissive light source technologies.
This means that the light emitted by the bulb is from the entire length
and radius of the bulb. Point
source of light technology means that the entire amount of light is emitted from
one “point source”. This
renders the wavelengths very intense and able to penetrate deeper with less
intensity falloff. Point source
light also produces glitter lines. This
effect is the same as what is produced by the sun in a pool.
They are very natural and attractive looking.
Recent research has concluded that they are also beneficial for corals
that live in very shallow water. They
are the “choice” light source for tanks greater than 24” depth.
Bulb replacement is less expensive than the other formats because (A)
they last longer; 16 - 24 months and (B) you need less bulbs to produce the same
quantity of light.
Many seasoned aquarists
eventually end up with MH
or HQI lighting.
Color
Light
is composed of different wavelengths. The
color of light is quantified using a temperature scale called
Kelvin. It is determined
by the temperature required to cause a solid black object to radiate a certain
color. For example, the midday sun
in the tropics is 5,500 degrees Kelvin. That
means for a black object to produce the same color as the sun, it would have to
be heated to 5,500 degrees. Many
different Bulb color choices are available.
They will all work. What
works best will be mostly determined by what looks
best to
you.
Ultraviolet Radiation
All
light bulbs emit ultraviolet radiation. PC’s
and VHO’s emit less than HID. Metal
Halide emits less than HQI. The
closer the bulbs are to the surface of water, then the more UV radiation that
will be transferred. The closer the
corals are to the surface of the water, then the more UV radiation they will
receive. Luckily, most corals have
a physiological response that allows them to protect themselves from excessive
UV radiation.
Many
of the intense and garish colors exhibited by shallow water corals are in
response to ultraviolet radiation. The
proteins that are produced by the coral are called Mycosporine-like
Amino Acids (MAA’s). The
ultraviolet radiation is reflected by the coral with the help of its’ MAA’s. The major drawback to promoting the production of MAA’s, is
the metabolic cost to the coral. This
means that you could have a smaller margin of error when it comes to the care of
your corals.
Infrared
Light
waves that are above the limit detectable to the human eye are termed Infrared.
They transmit heat. Corals
that are too close to the source of light can receive a high amount of infrared
light. The corals will protect themselves by producing Heat Shock
Proteins (HSP’s). HSP’s are
also produced at a metabolic cost to your corals and can also decrease your
margin of error.
Photoperiod
The
term photoperiod refers to the duration that the lights are left on.
On the reef, most corals receive 10-12 hours of light.
The intensity of light is not constant, but changing.
Slowly, the intensity increases in the morning with the rising of the
sun, and decreases in the afternoon with the setting of the sun.
This is not so easily achievable in our aquariums.
Most hobbyists are using more than one bulb and ballast to light their
reef. When this is the scenario,
the different lights can be on separate light timers.
This enables the aquarist to stagger the turning on and off of the bulbs
to mimic the rising and setting of the sun respectively.
The
duration of the photoperiod is different for different aquarists.
Corals require a minimum of 6 – 7 hours of light to fulfill their daily
photosynthetic needs. Any amount beyond that may lead to nuisance algae growth.
Each individual aquarist will have to experiment with their photoperiod.
The photoperiod can be 10 – 12 hours if it does not lead to the
excessive growth of nuisance algae.
Conclusion
These
are some of the different aspects of light.
Certainly the aquarist does not need to be familiar with all of them to
be successful. If you would like
help determining which lighting format would be most appropriate for you, then
come on in and consult with an AquaTouch employee.
Prepared by Scott Davidson
