Lighting the Reef Tank:
A Primer for Beginners
The subject of reef tank lighting is one
of the most controversial subjects in the reef keeping hobby.
Lighting is often a hotly debated topic on Reef Central, because
there are people who have had success or failure with each
different type of lighting system used in the hobby. The most
important consideration for reef tank lighting lies in choosing
a lighting system based on the requirements of the animals
that we wish to keep. While many reef keepers are concerned
with the appearance of their reef tank, their main concern
should be the health of the light requiring animals that they
are attempting to keep. As many corals and other animals have
symbiotic zooxanthellae that utilize light energy, the lighting
system must meet those animals' needs, both in terms of intensity
and color spectrum. The definitions of intensity and color
spectrum are beyond the scope of this article, but I will
include some useful references at the end of this article.
The commonly used phrase, "watts per
gallon," is a way of expressing the lighting necessary
for a tank by the ratio of the power used to illuminate the
tank divided by the tank size in gallons. Many hobbyists suggest
that an adequate amount of light would vary between four watts
and six watts per gallon for low light coral and as much as
ten watts per gallon (or more) for light loving coral. While
such a rule of thumb may initially sound like a good idea,
it should only be used as a rough guideline and not as a strict
rule. Obviously, such a loose rule is misleading, and aquarists
need to consider more than just "watts per gallon."
Specifically, they must take into account the height and overall
size of the tank. A tank that is 36 inches tall will require
more light intensity to reach corals on the bottom than it
would with a tank that is only 24 inches tall. For example,
all 120 gallon tanks would require 480 to 720 watts of light
based on the "watts per gallon" guideline, regardless
of their depth, so a 120 gallon tank that is two feet tall,
by four feet wide, and two feet deep would seem to need the
same lighting as a 120 gallon tank that is three feet tall,
by two feet deep, and three feet wide. The second tank, however,
is a foot taller. Since the intensity of light decreases as
the square of the distance from the light increases, the amount
of light needed is much greater if the same corals are to
be kept on the bottom of each tank.
There are many different types of lighting
systems available to the reef keeper. They can be simple fluorescent
tube lights, newer compact fluorescent lights or metal halide
lighting. All of these lighting systems have advantages and
disadvantages, but each may be successfully used to light
a reef tank.
Fluorescent lighting has been successfully
used by reef aquarists for years. Two common forms of standard
fluorescent light bulbs, normal output bulbs and very high
output, are used in the hobby today.
(1 - Actinic & 1 - Daylight)
Normal Output, or "NO," bulbs
refer to the amount of power (in watts) used to illuminate
the fluorescent tube. A standard NO ballast used with a 48-inch
tube will use 40 watts to produce the light from the bulb.
The following table depicts the wattage output based upon
the length of the NO fluorescent tubes.
The main advantages of NO lights are that
they are commonly available, the parts (such as ballasts)
are inexpensive, and the heat output of the lamp is fairly
low. The main disadvantage of this type of lighting is that
they produce little in the way of intensity in comparison
to other types of fluorescent lighting. Aquarium inhabitant
needs may require many tubes be placed over the length of
the tank. The increased number of ballasts required for such
a set up, if not mounted remotely, will add to the weight
of the lighting fixture, and the heat produced by the additional
ballasts may be significant and necessitate additional cooling.
Using an electronic fluorescent ballast with these tubes,
instead of the standard tar and coil ballast, can save electricity,
heat and weight, but the initial cost is greater. Additionally,
with the use of some electronic ballasts, the bulb intensity
may be increased over a traditional tar and coil ballast.
Perhaps the best application for NO tubes
are on short (18 to 20 inches or less), low light reef tanks,
but the choices of which coral to use with this arrangement
are very limited. Tanks using this lighting system typically
house low light requiring mushrooms, certain soft corals and
possibly some LPS corals that would need to be placed high
in the tank close to the light. I have personally kept tanks
using NO fluorescent lighting with some limited degree of
success. The tank consisted of soft corals and mushrooms requiring
only minimal lighting. While the corals did survive, their
rate of growth was slow.
Very High Output
The second form of standard fluorescent
lighting is Very High Output (VHO) fluorescent lighting. These
tubes require a special VHO ballast capable of handling the
higher wattage requirements. Although they appear similar
to NO tubes, their power usage and intensity is roughly three
times greater. For example, a four-foot VHO tube will produce
110 watts of light in the same space as a 40 watt NO tube.
The following table depicts the wattage output with the length
of the VHO fluorescent tubes:
With this increase in light output comes
additional heat, which can be easily dissipated by using a
simple box fan or two in the tank hood or fixture.
The main advantages of VHO lighting are
the high light output and the even spread of light over the
entire tank, when proper length bulbs are utilized. The disadvantages
of this type of lighting are that the cost for the ballasts
is higher than the cost for those used with NO tubes. The
heat created by the VHO tubes is also higher than NO bulbs.
With their higher light intensity, a greater variety of corals
can be kept under VHO tubes, including most soft corals, most
LPS corals and even many light-loving SPS corals. Such VHO
lighting works well on tanks that are less than 24 inches
tall. One of my most successful reef tanks utilized VHO lighting,
and I was able to keep a great variety of corals including
some SPS corals. The soft coral and LPS growth was amazing.
The SPS corals did grow well, although they were placed in
the upper third of the tank.
under 440 watts of VHO light
75 gallon reef
with VHO lighting
Fluorescent Ballast Options
There are two types of ballasts available
for fluorescent tubes: 1) core and coil ballasts and 2) electronic
ballasts. The common ballasts that come with the standard
NO and VHO bulbs and strip lights are core and coil ballasts.
They are somewhat heavy, produce some heat and use more electricity
than electronic ballasts. The electronic ballast does initially
cost more, however, the savings in electricity and minimal
heat output is, generally, well worth the initial cost. Electronic
ballasts weigh far less than the core and coil ballasts, which
allows more versatility in placement options. One particular
model of electronic ballast, made by IceCap, Inc., can
power both NO, VHO and power compact tubes in various combinations
with up to four bulbs. It is claimed that the longevity of
the fluorescent tubes is better when using the electronic
ballast over the core and coil type ballast, but many reef
keepers replace the tubes every six months anyway due to a
shift in spectrum as the bulb ages.
Fluorescent Tube Color Options
There are quite a few different color spectrum
options available in fluorescent tubes, with the most common
being full spectrum, actinic and 50/50 (which is a combination
of both). The most popular fluorescent tube color spectrums
are: the daylight, 6500 Kelvin bulb that is normally recommended
for SPS or clam tanks when enough tubes are used to create
the proper intensity. The next is the combination Actinic
and daylight bulb (a 50/50), which is equivalent to a 10000-Kelvin
bulb and is well suited for soft coral and LPS tanks. The
last bulb, called Actinic, is often used in combination with
other bulbs to give a fluorescent glowing appearance to green
and blue corals. Even though these tubes are recommended by
various bulb manufacturers for high light applications, you
must ensure that the light system is producing enough intensity
for the corals that you wish to keep.
Since the price of aquarium grade fluorescent
tubes is very close for both NO and VHO, the combination of
the electronic ballast along with VHO tubes is a better value
over NO tubes based on the amount of light output per dollar.
Power Compacts (PC), also known as Compact
fluorescents, are one of the newer additions to reef tank
lighting over the last few years. This type of lighting employs
fluorescent technology similar to VHO but instead of being
a long tube with a connecter on each end, it is folded in
half, giving it a "U' shaped appearance, and is powered
from only one end. It is suggested by various manufacturers,
that a 55 watt power compact bulb produces as much light output
as a 95 watt VHO tube.
Power compact lighting
The main advantage of the
power compact lighting is that it allows more wattage within
a smaller space than other fluorescent tubes, hence the term,
"power compact." Power compact lamps come in wattages
ranging from nine watts to 96 watts. The disadvantage of power
compacts is that there are not as many color temperatures
offered as there are with VHO tubes, although improvements
are continually being made in this area and bulbs with different
color temperatures are coming into the market.
Although, I have not had extensive experience
with power compacts, I have used 55 watt 6700 Kelvin bulbs
over one of my tanks. The light was very bright, however,
the fixture was very warm when compared to the VHO tubes that
I used on that same tank afterwards. A muffin fan should remedy
this problem and cool things off considerably.
If the many posts on Reef Central and other
message boards are any indication, metal halide lighting is
considered by many reef keepers to be the ultimate lighting
for a reef tank. There are many different wattages and color
spectrum choices. When proper wattages are used, almost any
light-loving coral may receive proper illumination. The main
advantage of metal halide lighting is that the bulbs are very
bright and are the best option available to reef aquarists
intent on simulating natural sunlight. These bulbs are available
in wattages ranging from 50 watts to over 1000 watts. Some
of the more common wattages used in the reef keeping hobby
include 175 watt, 250 watt and 400 watt bulbs. Metal halide
bulbs come in a wide variety of shapes, wattages and colors.
Along with all of these options, comes a great deal of confusion
when choosing this type of lighting for a reef tank.
400 watt metal halide
bulb on top of a ballast
Even though metal halide lighting sounds
like a reef keeper's panacea, they do have one major disadvantage.
Metal halide lamps (and some ballasts) produce an incredible
amount of heat. The heat of these bulbs will easily burn the
skin off your arm even if only touched lightly; I have the
scars to prove it. This heat is transferred into the reef
tank water and the room in which the tank is located, unless
fans or other forms of cooling/ventilation are employed.
Unlike fluorescent tubes, which diffuse
light fairly even across the tank, metal halide lamps are
more directional in nature. The most intense light is found
in the area located directly below the lamp. As you move from
directly below the lamp to the sides, front or rear, the amount
of light decreases with distance. Because of this decrease
in intensity, Metal halide bulb manufacturers recommend that
one bulb be used for every two-foot square area of tank surface.
As an example, this would require two bulbs over a four foot
long by two foot wide tank in order to achieve proper coverage.
Since this light is more directional than other types considered,
this type of bulb is useful on taller tanks or tanks where
a large amount of light is needed to satisfy light-loving
animals such as clams and SPS corals.
There is no rule of thumb when it comes
to metal halide wattages, but there are some general guidelines
to follow when choosing what watt bulb to use. On tanks 20
inches or less in height, one 175-watt metal halide bulb per
two square feet of tank surface area will satisfy most corals'
needs, as well as those of clams. For tanks over 20 to 30
inches tall, 250-watt metal halide bulbs will suffice. On
tanks over 30 inches tall the 400-watt versions are useful
for providing the appropriate intensities at the tank bottom.
Now here comes the twist. Many reef keepers use higher wattage
bulbs on relatively short tanks. It is not uncommon to see
reef tanks under two feet tall using 400-watt metal halide
bulbs in clam and SPS coral dominated tanks. I use 400-watt
metal halide bulbs on my 90 gallon, 24 inch tall mixed reef
tank with great success. The extra wattage helps ensure that
my SPS corals, some of which are placed on the bottom of the
tank, receive enough light. One other thing to take into consideration
is that you can have too much light for certain corals and
a great many other animals. Some large polyp stony corals
often do not take well to intense light and need to be placed
so that they are either somewhat shaded or located near the
bottom of the tank.
Along with different wattages, different
color spectra are available for metal halide bulbs. As is
true with all bulbs, their color temperature is measured in
degrees Kelvin (K). In simple terms, the higher the Kelvin
rating, the bluer the bulb will appear. Since we are trying
to meet the photosynthetic requirements of our corals, we
want to give them the proper color spectrum to ensure their
health and growth.
|Standard Incandescent Bulb
*Color temperatures below 5500 Kelvin
are not commonly used in reef aquariums.
When it comes to metal halide color spectrum,
there is no one general rule of thumb, but some general observations
can be made. Many hobbyists use metal halide bulbs with a
Kelvin rating of 6500, and these bulbs produce a warm yellow/white
appearance that simulates the midday sun on a shallow reef.
Bulbs of this color are well suited for high light demanding
corals and clams. While hobbyists report great success using
these bulbs, they often complain of their yellow appearance
when used without supplemental actinic light. Another common
bulb is the 10000-Kelvin bulb, which produces a white appearance
with a slight hint of blue. Although many hobbyists have also
had good results using these bulbs over most types of corals,
some have noticed that coral growth rates are somewhat slower
than those using 6500-Kelvin bulbs. Gaining much wider acceptance
and use lately is the 20000-Kelvin bulb, often called a Radium,
which has a blue colored appearance. These bulbs are better
suited for deeper water soft corals and LPS, although many
hobbyists have also had success using them over clams and
I have personally used all of the above
Kelvin bulbs with the following results:
The 6500 Kevin bulbs have given me the
greatest coral growth in SPS, LPS placed lower in the tank
and even soft corals. The color of the 6500-Kelvin bulbs when
supplemented with actinic VHO tubes produces a crisp white
appearance. For those seeking the greatest growth rates from
SPS corals, I would recommend this color bulb.
The 10000-Kelvin bulbs also achieve good
growth rates, albeit slower than the 6500-Kelvin bulbs. Their
appearance is white with a slight blue tint when used with
actinic supplementation. Bulbs of this color have produced
excellent growth with soft corals and LPS in my own tanks
along with slower paced SPS growth. I would recommend this
bulb for a mixed reef environment.
The 20000-Kelvin bulb is very blue and
brings out all of the fluorescent pigments in many corals.
While they are visually appealing, the growth rate of my SPS
corals came to a complete standstill while using them. I feel
that these bulbs are well suited for a tank that simulates
a deeper reef environment with LPS and soft corals but from
my own experience, I do not feel that they are the best choice
for high light SPS and clams. One note about the 20000-Kelvin
lamps: in order to get the best intensity and color from these
bulbs, they require a special HQI ballast for them to be driven
as intended. This ballast is similar to the standard metal
halide ballast, but includes a special starter to fire the
Metal Halide Ballasts
Metal halide lights do require ballasts
and as with the fluorescent bulbs, the common options are
the core and coil ballast and the electronic ballast. Where
reliability and performance are concerned, the electronic
ballasts have received mixed reviews amongst reef keepers.
While some hobbyists have had success with electronic ballasts,
there have been issues with the ballasts under-powering bulbs,
interfering with TV and radio reception and problems arising
from less than perfect home wiring. The electronic ballast
may also interfere with the popular X10 wireless controllers
that many hobbyists use with their reef tanks. Also, the initial
cost of the electronic ballast is higher than the core and
coil ballast; however, this can possibly be compensated for
in terms of its electricity cost savings over time.
Dual 400 watt metal
(Core and Coil)
The core and coil ballasts are very large,
heavy and create a significant amount of heat. These ballasts
also use a great deal of electricity. The advantage to this
type of ballast is that they are normally very reliable and
are typically less costly than their electronic counterparts.
Another common practice among reef hobbyists
is to combine different forms of lighting to achieve the proper
spectrum and intensity in the reef tank. Many hobbyists use
metal halide bulbs along with Actinic fluorescent tubes to
satisfy the requirements of the corals and obtain an appearance
that is visually appealing. A common example is the use of
6500 Kelvin bulbs with Actinic fluorescent tubes. The Actinic
tubes offset the yellowish appearance created by the Iwasaki
bulbs and bring out a crisp white appearance. There are many
other combinations possible and, unfortunately, it takes experimentation
to find a combination that produces good coral health while
still being aesthetically appealing.
Unfortunately, there is not one particular
lighting system that will ensure success for all corals that
many hobbyists want to keep. As long as the hobbyist does
his/her best to match the requirements of the corals with
the type of lighting system, this will go a long way towards
I would suggest finding other reef keepers
in your area who have the type of lighting systems that interest
you and go see their tanks with your own eyes. Look for the
overall appearance of the tank, the health of the corals and
the placement of corals in relation to the light. Also, ask
many questions on message boards such as Reef Central, since
many hobbyists have already gone down this road, and can give
advice based on their experience using various lighting combinations.