Freshwater
Tropical Aquarium Fish Lighting
Part 4
The following article was written by Mr.
Richard Sexton.
June 17, 1998
While mostly aimed at aquarists, this
article is also applicable to other people interested in growing things
under artificial light.
HID LAMPS
Now we're getting serious
HID or High Intensity Discharge are the big bright lamps you see in
grocery stores, street lighting and industrial lighting. They can be very
large and draw a lot of power. Indeed 2000 watt and 6000 watt lamps exist,
however small ones, down to 70 watts are available.
Tradeoffs
These lamps produce a lot of light output quite efficiently, however
they can be quite expensive to install initially and may require a fan for
cooling in the housing/reflector as they can produce phenomenal amounts of
heat. These lamps are used by aquarists who need lots of light, such as
marine reef tanks, of large freshwater plant tanks.
HID lamps requite a ballast, and almost every bulb requires it's own
type of ballast. The ballasts are expensive and bulky and are not
something you trot on down to the corner hardware store to pick up,
although larger hardware stores may have some; they are usually reasonably
priced. You'll have to go to a lighting supplier for most of them however.
HID lamps are built like halogen bulbs. A small capsule contains the
vapour that an arc is sent through. This capsule is in turn encased in the
much larger outer bulb body. There is quite a bit of UV generated by the
inner capsule that is filtered by the outer capsule. All these bulbs carry
warnings not to operate them if the outer capsule is broken.
Types
There are three basic types of HID lamps: mercury vapour, sodium vapour
and metal halide.
Mercury vapour
When you see a bright light illuminating some industrial building and
it has a decided bluish cast - that's mercury vapour. Mercury vapour lamps
have an output spectra that is almost entirely blue-white, with very
little red. Worse, the spectra is not continuous, there are spectral peaks
at certain wavelengths. These lamps, although not useless - there is no
doubt very good results can be obtained with them - are equivalent to cool
white fluorescents. Yes they work, but why bother going to this expense
and trouble when other bulbs will yield much greater success?
One interesting variation on this theme is the self ballasted bulb.
These bulbs (around 250 watts) require no ballast, they just screw into a
standard medium base (ie. incandescent) fixture and voila, light. The
downside is these bulbs are not as efficient as regular mercury vapour
lamps because they use the resistive properties of the large filaments as
a ballast, and worse of all these bulbs are very expensive, around $100
plus or minus $30. Of course with mercury vapour lamps having a 10,000
hour lifespan the high cost of the bulb must be considered in view of the
lack of expense for a ballast.
Sodium vapour lamps
These lamps come in two varieties, high pressure sodium and low
pressure sodium, although this is rather a moot point, as the light they
output is monochromatic (pure) yellow, and is all but useless in terms of
aquaria. It's rather a shame, as they are a full ten times more efficient
then incandescent bulbs, in fact these are the most efficient bulbs made,
and have a 24,000+ hour lifespan. These are one of the cheapest HID bulbs
to purchase, and can be found in most hardware stores for around $80 for
bulb and ballast. Spare bulbs are around $30. Recent advances in high
pressure sodium bulbs such as the Philips "Sun Agro" have
improved output spectra, and are quite popular for terrestrial plants,
although they havn't as yet gained great acceptance with aquaric
gardeners.
Metal Halide
Like sodium vapour, these lamps come in two versions, regular and
colour corrected (HQI) versions. The HQI versions have a uniform, sunlight
like output spectra, whereas the standard halide bulb has a lot of yellow,
some blue and not much red. Unlike sodium vapour, these lamps are very
useful to the aquarist needing a lot of light. They can be found nominally
in 250, 400, and 1000 watt sizes, from most manufacturers, but Osram also
makes a 70 watt and a 150 watt size. The 70 watt bulb is only 2 x 3
inches, although is unfortunately a 3000K colour temperature bulb. You
have to go to a 250 watt bulb to get 5400K colour temperature.
These bulbs range in life from 6000 to 10,000 hours. Bulbs are around
$50, ballasts are around $100.
Some sample setups
Obviously with a plethora of different type of lighting systems to
choose from, trying to figure out what tube to use can be a nightmare.
Largely it depends on what you are trying to illuminate, and what your
budget it.
It also depends on what size tank you are trying to illuminate, not so
much as surface area or footprint of the tank, but depth of the water. The
example setups below are for four 15 gallon tanks turned sideways so that
a four foot fixture across the top will illuminate all of them. Double the
amount of light for deep tanks greater than 18 inches.
Many small aquariums have a small plastic or metal hood that has one or
two tube shaped incandescent bulbs. For the bulbs to provide enough light
to grow plants they need to be of such high wattage that there will be a
severe and deleterious effect of the fish by the massive amount of heat
being given off from the bulbs.
Incandescent illumination, although inexpensive in initial setup cost
is not recommended for aquaria. The heat generated by these light bulbs
almost always adversely affects the temperature stability of an aquarium.
The cost to operate is fairly high, and the quality of light is poor
compared to every other lighting system. Having said that I have seen some
setups using incandescent lights that worked well. Plants were healthy,
the tanks were not that hot. Be that as it may, if you get good results
with incandescent lights you will get better results with fluorescents.
Some of the smaller halogen bulbs are useful for supplementing fluorescent
lights, as the halogens, because they are still incandescent, put out
quite a bit of red light. Not only does this help to balance the spectrum,
but it has a more pleasant aesthetic appearance.
Theoretically a 300 or 500 watt halogen lamp can be suspended a foot
above the tank, and this would provide enough light without cooking the
fish, but 500 watts is a lot of energy; a 175 watt metal halide bulb will
provide the same amount of light for a lot less energy. The only practical
use for incandescent lights would be in a setup that was primarily
fluorescent. A couple of small halogen bulbs, if well shielded from water
splashes would provide the red light so needed by plants.
Fluorescent lights are the most economical way of lighting an aquarium
in the long run. Once the initial purchase of the fixture is made the low
cost of operation and long life of the tubes makes fluorescent light very
attractive. For a beginner tank that has an incandescent fixture the new
compact fluorescent bulbs with integrated ballasts will, in many cases,
screw right into the existing incandescent ballast. Bulbs for these are
available from 2700K to 5000K colour temperatures, although as of this
writing only Osram makes 5000K compact fluorescents.
The absolute cheapest setup is to buy whatever fluorescent tubes are on
sale at the local hardware store. Usually cool white. This is far from the
best, but it will work. One cool white and one warm white is a little
better, although one plant growth light and one daylight bulb is still a
fairly cheap setup, (both are well under $10) with quite good light
quality.
For growing plants, a setup consisting of one plant light, two wide
spectrum plant lights and one chroma 75 (or equivalent) will provide the
right amount of the correct type of light. Triton (or equivalent) tubes
could be used of cost is no object. If the pinkish colour is
objectionable, two Ultralume 3500 and two Ultralume 5000 can be used
instead of the wide spectrum plant lights.
For keeping African Cichlids, or any other fish that is used to a lot
of light, two (or four, depending on preferences) chroma 75's can be used.
Low light fish such a killifish and dwarf Cichlids will do best under
two Gro-Lux or if they have an abundance of plant cover, two Gro-Lux wide
spectrum tubes. These tubes will not frighten the fish with a lot of
light, and they should encourage good plant growth to provide much needed
cover from the light. As an aside, I have kept certain killifish such as
Aphyosemion australe, A. gardneri, and A. sjoestedti under the setup
described above for plant growth and they didn't seem to mind. Some
species of fish do not like a lot of light and in the wild will hide under
cover to avoid intense light. In an aquarium with bright light and without
some cover to take refuge they will be as stressed as if they were forced
in the wild from their shady environ to an area on bright light.
Marine invertebrates and certain freshwater plants have very large
light requirements, and for these, an HID lamp would probably be the most
appropriate. It is unlikely you could put enough fluorescent tubes on top
of the tank to supply enough light, or if you could you may have spent so
much on VHO lamps and ballasts that it would have been cheaper to install
a halide lamp in the first place.
The cost of the HID lamps is pretty large, and even worse, the more
useful lamps to growers of plants are even more expensive. Usually mercury
vapour or sodium vapour lamps are available at semi- reasonable rates from
hardware stores where they are sold as security light; especially in rural
areas. I have heard of people trying sodium vapour lamps, but have never
heard of any success with them. People have had some mixed success with
mercury vapour lamps. Metal halide lamps give very good results, but are
the most expensive and difficult to obtain of all the HID lamps.
For applications requiring a REALLY BRIGHT light, the current GE
lighting catalog lists a 10,000 watt carbon arc lamp used for lighthouses.
Summary and conclusions
Like everything else in life you get what you pay for. Lighting systems
can be built from apple juice cans and incandescent fixtures for almost
nothing, or the latest and greatest in aquarium HID lighting can be
ordered from Germany.
For most people, fluorescent light will be the reasonable compromise
between cost and quality of light. For a little bit of effort, the
specialized fluorescent tubes can be sought out with only a little bit of
time and a bit more money than the ubiquitous cool whites hanging over the
workbench.
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