Fig
1: Aquarium Lighting's moon-light illuminates a strand of
fiber-optical cable
About
two years ago I met Ken Green of Concept Lighting. He is a Cichlid
breeder who also happens to design and sell industrial lighting
systems. He helped me in the selection of the lighting system for
my 2000 gallon tank (see the 2002 Marine Fish and Reef Annual for
details). He and I began talking about fiber-optics lighting and
working together we assembled a system that we could experiment
with to learn whether fiber-optic lighting was practical in a reef
tank. While experiments continue, I thought it time to share what
we’ve found so far to encourage others to explore the
possibilities of adapting fiber-optic systems for lighting a reef
tank.
Working with Mr. Green, we assembled a
system that I will outline below to demonstrate some of the
possibilities. The system was assembled from “off the shelf”
components, but the parts were not designed for reefkeepers, so
don’t expect to find these systems showing up in fish stores
anytime soon. Given aquarist’s history for modifying and
adapting products for use in the hobby, hopefully this report will
prompt sufficient interest in the approach so that companies like
Concept Lighting will sell to the hobby.
Fiber-optics has its own jargon that refers
to the various components making up a lighting system.An illuminator is the light source that generates the
light. The illuminator is a box containing the light source, a
ballast when necessary, and a fitting that mates with the optical
cable. The fitting that couples the optical cable to the
illuminator is called a fiberhead. The fiberhead combines one or
more fiber-optic cables (figure 2). The close-up in figure 3 shows
the individual fibers sealed in a fiberhead. The fiber cables used
in industrial lighting design are of different design from those
used for telecommunications. The “glass” fibers are actually
plastic. They are more flexible, less fragile, and less expensive.
Fiber optic cables are typically rated in strands, which is the
number of individual fibers in a jacketed cable. It can range from
25 to 75 or more strands in a single bundle. Most illuminators can
handle multiple bundles, so a typical illuminator might have a
capacity of up to 500 strands which might be made up of a large
number of small capacity cables or a smaller number of large
cables.
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Illuminators in the past have used quartz
halogen light sources so they suffered from relative low efficiencies
and low color temperatures in the range of 2500-3000 degrees Kelvin.
However, new designs are coming out using 150 watt HQI single ended
metal halide bulbs. Thus far the available metal halide bulbs have only
been rated at 4000 K, but as I’ll show shortly, the rating appears to
be conservative. The good news is that the bulbs are rated for 10,000
hours. These appear very similar to the metal halide bulbs used in LCD
projectors (figure 4).
Evaluating a fiber-optic system has proved
to be a challenge. One does not use a fiber system in the same way one
might use a fluorescent bulb or metal halide system, so comparing these
results to published reports of other lighting systems should be made
with caution. Measuring the intensity of the illuminator two feet away
from the bulb as I have measured metal halide bulbs produces PAR of 246
mE/m2/sec. This compares to 165 mE/m2/sec for the Iwasaki 400 watt
bulb evaluated in my May/June 1997 Aquarium
Frontier’s article.
One might conclude that the illuminator
generates more intense light than a 400 watt metal halide bulb. In a
literal sense it does. However, the illuminator uses an integrated
dichroic reflector, so one is comparing a bare single ended metal halide
bulb to the intensity of a 150 watt bulb with integrated reflector. (A
similar confusion has fueled the notion that a double ended 150 watt HQI
metal halide bulb generates more light than a single ended 400 watt
Iwasaki bulb. Next month this column will review a new double ended bulb
and ballast and address this issue in much greater detail.) Color
temperature measures 6000 degrees Kelvin and the light quality is very
reminiscent of an Iwasaki 250 watt metal halide.
The key measurement for comparing
traditional lighting systems to a fiber-optic system is how well
the illuminator and fiber-optic cable maintain intensity as
distance from the bulb increases.The problem is that the intensity depends on the number of
cables and how they are configured. Using a single 500 fiber cable
ten feet in length, the intensity at the end of the fiberhead
exceeds the capacity of the LiCor Datalogger, which is greater
than 10,000 mE/m2/sec, or five times the intensity of equatorial
noon-day sun. At two feet from the end of the ten foot cable the
light intensity is 86 mE/m2/sec. This means that twelve feet from
the light source the light intensity is still 60% greater than
that of a bare Ushio 175 watt bulb measured at two feet from the
bulb. A second more practical configuration I have been working
with is separate multiple bundles so that a large area of a tank
can be illuminated. For this configuration I’m using 50 strand
cables fit with underwater lens designed for use in swimming pools
(figure 5). With six separate cables, the light intensity at each
lens exceeds the capacity of the Li-Cor Datalogger. Even at one
foot from the lens, each of six strands is generating an intensity
of 68 mE/m2/sec. This intensity is at the end of six separate six
foot bundles all illuminated by the same 150 watt metal halide
bulb.
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The underwater lens is intriguing because
it enables one to place the fiber-optic cable underwater. A source of
light loss is the distance from the tank’s water surface where a metal
halide has to be placed. Generally, the bulb is placed a half foot or
more from the surface of the water. Light is reflected off the surface
of the water, so intensity in the tank is considerably less than the
bulb generates. With the underwater lens, the lighting system can be
essentially placed underwater, reducing light losses due to distance and
light reflecting off the water.
High intensity lighting generates a great
deal of heat. Placed close to the water surface, metal halide bulbs can
increase water temperature by several degrees. Another intriguing aspect
of fiber-optic lighting is reduced heat. The temperature at the lower
edge of one of my 400 watt pendants approaches 100 degrees Fahrenheit
over ambient air temperature. The 500 fiber fiberhead runs ten degrees
cooler despite the higher light output. No increase in temperature over
ambient is found with the underwater lens.
Fig
2: Two fiberheads combine multiple fiber cables
Fig
3: Individual strands are clearly visible in the fiberhead
Fig
4: A 150 watt metal halide bulb with integrated reflector
Fig
5: Watertight fittings protect the fiber optic cable
The more one learns about fiber-optic
systems, the more one realizes that fiber-optics open up many new
possibilities. For example, lighting hoods typically add one to two feet
in height to a reef tank. With fiber-optic lighting, there is no longer
a need for a lighting hood. The light source can be mounted any place
near the tank, even under it. I’ve been working with ten feet lengths,
but up to twenty feet cable lengths are practical, particularly if one
uses the underwater lens. This means one could mount the illuminator in
another room.
There
are a great many issues to be worked out. I’ve illuminated corals
for short times with the fiber-optic system, but I have yet to do
long term studies. The flexibility of fiber optic lighting raises
philosophical issues. For example, using six 50 strand cables, I can
illuminate a 55 gallon tank more evenly than one can with a single
150 watt metal halide bulb. However, one key question is whether it
is more important to evenly illuminate an entire tank or create
higher peak intensities in some portions of the tank. My work thus
far also raises the question of hybrid systems. For example, one
option is to direct the output of a fiber-optic light source into a
specular reflector. This would allow us to use remote light sources
while retaining the light spread found in current systems. The small
integrated reflector metal halide bulbs might be used for reef
systems even if we do not use fiber-optics. Should the hobby be
examining the small metal halide bulbs used in LCD projectors and
illuminators? And, what about creating our own illuminators using
higher Kelvin metal halide bulbs? Why not create illuminators
specifically designed for reef tanks? There are many such questions
and few answers, but I hope this progress report has generated
sufficient interest for others to begin exploring the possibilities
