Artificial lighting
by Richard Sexton
Introduction
There are a number of different approaches used
for illuminating aquaria. To make an informed
decision as to what type of lighting should be
employed, the fundamentals of light, color and
lighting systems should be understood. In this
article we will examine the how light is
qualitatively appraised with respect to color
and intensity. Different lighting systems will
be examined, and most available types of lights
will be discussed. Examples of some "real world"
lighting systems will be given and analyzed with
respect to effectiveness, initial cost,
operating expense and longevity.
Light and color
What is light?
Visible light is that part of the
electro-magnetic spectrum that lies between the
wavelengths of ultraviolet and infrared. That's
probably more that you need to know for the
purposes of home aquaria.
White light is all
colors
When we see a rainbow, we are seeing white light
split up into it's component colors, hence the
expression "all the colors of the rainbow".
Sunlight is different in different places in the
world Sunlight contains, more or less, equal
portions of all colors of sunlight. Northern
sunlight, that is, sunlight in areas north of
the fortieth parallel, has more blue than
equatorial sunlight because of absorption of all
other colors, or wavelengths of light, by the
atmosphere.
Blue pictures
underwater
This is the same effect that causes underwater
photos taken below three feet to be so blue.
Just as the atmosphere absorbs non-blue light so
does water, except water absorbs non-blue light
at a much greater rate. Almost all non-blue
light below three feet of water is absorbed. How
is light measured?
Light
quality is expressed and measured in many ways.
Light color can be measured in degrees Kelvin
(K) and the color rendering index of a light
source can be measured and expressed as CRI.
Color temperature -
degrees K
White light can have different "warmth". A bit
more red/yellow and white light appears
"warmer". A bit more blue and light appears
"cool". This can be quantitatively assessed by
the assigning of a color temperature, given in
degrees Kelvin. Think of color temperature as
the color of a block or iron as it is heated to
various high temperatures. A warm, reddish light
is around 3500 degrees Kelvin, and above 6000
degrees Kelvin the light takes on a bluish tone.
Sunlight is somewhere around 5000 degrees
Kelvin. The first part of the paragraph is
misleading. Although people may think of blue as
a "cooler" color than red, it is actually
hotter. For the physicists out there, iron is
acting as a black body here.
Color Rendering
Index (CRI)
The color rendering index identifies the degree
of color shift objects undergo when illuminated
by a particular light source. In simpler terms,
the CRI expresses the degree to which a light
source renders the true color impression. The
CRI is an index and ranges from 0 to 100. A
light source having a CRI of 100 means objects
illuminated by it look like they're supposed to;
that is their natural color is not distorted. A
light source having a very low CRI would tend to
make objects appear to be a different shade or
even color that they really are. An example of
light with a high CRI is, obviously, sunlight.
Some fluorescent tubes such as Daylight, Chroma
65 or Vita-Lite have a very high CRI. Some light
sources such as Gro-Lux or sodium vapor lamps
have very low CRI's.
Natural sunlight
Good light, free, but hard to control
This is of course what fish and plants are used
to, and it can hardly be argued that this is
anything less than the most natural. However,
coaxing enough sunlight into your aquarium, from
the top, rather than through the sides,
throughout the whole year, can be problematical.
Sunlight is the certainly the cheapest way to
illuminate an aquarium, although it is
unreliable and very difficult to regulate. This,
of course is subject to geographical variation.
If you live in California and have a skylight
over an aquarium, you might be getting enough
light. If however, you live in an area that does
not get a lot of sunlight, and your aquaria are
stacked in rows in a basement you will obviously
need supplemental lighting.
Very
few people use sunlight as a primary lighting
source, although it is often used as
supplemental lighting. Scrutinizing the photos
of the 10,000 liter Dupla tank in the Horst and
Kipper book _The Optimum Aquarium_ you may
notice that besides having a number of powerful
Metal Halide lamps there are skylights for
auxiliary lighting.
Incandescent
lighting
Cheap, low quality light
Incandescent lights are the ubiquitous screw-in
bulbs you most likely have lighting your home.
An Incandescent bulb consists of a glass bulb,
with a tungsten filament in a near vacuum; just
a small amount of argon or krypton is present.
When current flows through the filament it heats
up, and glows giving off both heat and light.
Halogen bulbs
A variation of the incandescent bulb is the
halogen bulb. This is an improvement to
incandescent bulbs invented by GE in 1958 for
the wing tip navigation lights of the Boeing
707. In a regular incandescent bulb, the
tungsten filament evaporates, and over time the
inside of the bulb is coated with a fine coat of
tungsten from condensed tungsten vapor. This
coating will severely limit the light output of
the bulb. In a halogen bulb, a small amount of
one of the halogens (Iodine or Bromine are used)
is present and combines with the evaporated
tungsten. This Tungsten Iodide or Tungsten
Bromide molecule has an affinity for the
tungsten filament, and returns there and splits.
The tungsten from this molecule returns to the
filament while the halogen returns to the
atmosphere inside the bulb. This process does
not work unless the bulb jacket is at least 200
degrees Celsius. This is why halogen lamps are
so hot, and must be taken into consideration for
aquarium applications. Halogen lamps are 25-30%
brighter than regular incandescent bulbs. The
halogen cycle, as it is called, takes place in a
very small capsule, as it is easier to maintain
the high temperature required for the halogen
cycle to operate in a smaller space. This
capsule is placed inside another glass capsule
which serves as the bulbs outer casing and
although is still plenty hot, is not as hot as
200 degrees Celsius.
Output spectra is
biased towards the red
The output spectrum of incandescent light,
halogen or regular, is biased heavily toward the
red. Non halogen bulbs have a color temperature
of 2700K, while halogen bulbs have a color
temperature of 3000K - they are a slightly more
whitish light. Both have a CRI of 100. A diagram
of the spectra looks rather like a triangle,
starting with almost no output in the green and
rising at an almost linear rate to the far red
and infra red. Although incandescent bulbs are
very inefficient, they are a very good source of
near and far red light which is certainly very
important. They are sometimes used as
supplements in systems which are deficient in
the red end of the spectra.
Efficiency
The two great disadvantages to incandescent
lights are their inefficiency - you don't get a
lot of light compared with how much energy you
put apply. One saving grace in this respect is
that the efficiency increases proportionally to
the wattage, for example a single 100 watt bulb
is much brighter than two 50 watt bulbs. The
energy that does not get converted to light is
wasted by being given off as heat. All but the
smallest wattage bulbs can generate an awful lot
of heat, and this must be taken into
consideration. Another point to consider is,
because the heat is so great, a splash of water
on a hot bulb can shatter it.
Halogen
bulbs are more efficient than "regular"
incandescent bulbs by virtue of remaining
brighter, longer; they still give off 95% of
their initial light output at the end of their
lives, which are about twice as long as regular
incandescent bulbs. They are also more
expensive. The great advantage of non halogen
bulbs is of course their extreme low cost for
initial purchase, and of course their great
availability; you can buy them anywhere. Halogen
bulbs are on the average 5 to 10 times as
expensive as their non halogen counterparts and
can usually be found at larger hardware stores.
Since their primary market is yippie track
lighting they are usually found as spot or flood
lights. Of potential interest to aquarist is the
low voltage bulbs used in some track lighting
systems. Operating as 12V, these bulbs are quite
small and would be good to use a supplemental
light augmenting a fluorescent setup. They are
also the cheapest of halogen bulbs. While I have
seen them at $30 each in fancy designer light
stores, I have also seen them in Price Club at 3
for $12. Sylvania makes a series of bulbs called
Capsylite that come in "regular" bulb shapes
plus the large parabolic reflectors sometimes
used to illuminate the outside of houses. Osram
makes a large array of different shapes and
sizes, most of which look like the vacuum tubes.
They are probably the most useful to aquarists
because of their smaller size and wide range of
wattages; from low power bulbs all the way up to
150 watts. They are however not cheap and can be
quite a challenge to find somewhere that stocks
them.
Longevity
Incandescent bulbs have a lifespan of about 1000
hours. Halogen bulbs have a life of about 2000
hours. One interesting personal note here;
although regular incandescent lights are rated
at 1000 hours, we've all had some bulbs that
seem to burn on forever. The Guiness book of
world records lists the longest lasting light
bulb as being an incandescent bulb in a fire
house in, I believe Boston that is some 70+
years old; it is never turned off, which is a
key point. This is why your parents always gave
you hell for flicking the lights on and off
really quickly, the wear on the filament from
having current suddenly shot through it is quite
great. If you'll notice, most bulbs fail when
turned on, not in the middle of operation, or
when they are turned off. The halogen bulbs I
have throughout my home seem to be on a timer;
when 2000 hours is up *poof*, they expire. I
curse them out, do a rough calculation and come
to the conclusion that their 2000 hours just
expired.
Flourescent lighting
Cheaper To Run, More Expensive To Install
Fluorescent lights are very common in our day to
day lives. They are cheap to operate as they
emit about four times as much light per unit of
electricity as incandescent lights do. On the
other hand they are more complicated to install
because they require a ballast to operate. You
may be familiar with the regular "cool white"
and "warm white" tubes sold in hardware stores
but what you may not know is that fluorescent
tubes come in hundreds of shapes, sizes and
spectral output.
How they work
Fluorescent lights work by placing an anode and
a cathode at opposite ends of a glass tube.
Inside the tube is a partial vacuum and a small
amount of mercury vapor. When energized, the
mercury vapor is ionized and emits ultraviolet
radiation. The inside of the tube is coated with
a phosphor - a powder that "fluoresces" (gives
off light) when stimulated by ultraviolet
radiation, thus producing visible light. The
chemical composition of the phosphor determines
the spectra or color of the emitted light.
Replace tubes every
six months
Although fluorescent lights are very energy
efficient, there is a particularly nasty
phenomenon known as "cathode decay" that causes,
over time, less energy to be transferred through
the mercury vapor. The net effect is that the
tube will emit less and less light as it gets
older. To all appearances, the tube will put out
the same amount of light until it suddenly stops
dead one day, (which can take years), but for
all practical purposes, because the drop off in
light output is an exponential decay, the tube
should optimally be replaced every six months or
at the very least once a year. Writing the
installation date on the tube itself with a
permanent magic marker can be a big help here.
Types of fluorescent
tubes
There are many different types of fluorescent
tubes. They differ in the physical size,
composition of the phosphor and the wattage.
When fluorescent tube is mentioned the standard
T12 four foot tubes usually comes to mind. This
tube has a diameter of 1.5 inches and is
available in 18", 24" 36", 48", 72" and 96"
lengths. The T8 or "slimline" fluorescent has a
1" diameter tube and is available in 24", 36"
and 48" lengths. T12 tubes are also available in
U-shaped, that is a four foot tube is bent back
on itself so it forms a large U, and is about
24" long. Circular tubes are available with
several different radii, and in several
different types. In the last few years, compact
fluorescent tubes have become very popular
mostly as replacements for incandescent bulbs.
These tubes come in all sizes, from a 3" 5 watt
bulb to much larger bulbs that replace 40W four
foot tubes, yet are just one third of the size.
The phosphor chemistry is what makes the
difference between a cool white and a daylight
tube and every tubes is available with a
dizzying array of choices in this area. Some of
the most useful tubes for aquarists with small
tanks are the 5000K compact fluorescent tubes.
T12 tubes are available in HO (High Output) or
VHO (Very High Output) which draw more and much
more current respectively, but reduce more light
than regular T12 tubes. As the composition of
the phosphor changes so does the spectra of the
visible light being emitted by the tube. For
aquarium use, whether for illumination for plant
growth or to simply be able to see inside the
tank only a small percentage of the dozens of
available tubes are appropriate. They fall into
the following broad categories: industrial, full
spectrum, daylight, plant growth, actinic,
tri-phosphor, special purpose and HO/VHO.
Use four foot tubes
Although fluorescent tubes come in many sizes,
volume of scale dictates that there is really
only one size - the T12 four foot length. Some
ninety percent of all fluorescent tubes made are
this size, and because of this volume, this is
the cheapest size, although this needs to be
qualified. If you are buying tubes through
normal retail channels, the markup is generally
high enough that they can play with prices and a
24 inch tube costs less than a 48 inch tube but
more than an 18 inch tube. If however you are
buying tubes through other channels, such as
lighting distributors, you may find that the
four foot tube is cheaper than any other size.
T12 tubes that are smaller or larger will cost
you more. Additionally, the four foot size has
the longest lifespan and also the highest ratio
of lumens (light output) per watt. Thus, where
space allows, use four foot tubes. If there is
not enough space for these, individual compact
fluorescents may be called for.
Manufacturers
In North America the "Big Three" in fluorescent
tube manufacturing are General Electric (GE),
Sylvania and Philips. They all make, almost
without exception, the same tubes, under
different trade names although there are some
notable exceptions. Smaller and off-shore
manufacturers include Duro-test in the US and
Osram who make some tubes in North America and
some in Europe. There are a small number of
specialty tube manufacturers aimed specifically
at the hobbyist aquarium market.
Industrial tubes
These tubes include the ubiquitous "cool white"
and "warm white" usually used in home and
industrial lighting applications. These tubes
are tuned to produce the brightest possible
illumination for the least amount of
electricity. Since the human eye is most
sensitive to green, these tubes peak in the
green portion of the visible spectrum. In fact
they rise and fall quite sharply either side of
the green peak. Warm white is shifted a bit
toward the red end of the spectrum thus
accounting for the "warmer" appearance.
If
all you want to do is illuminate your tank these
tubes are fine. These tubes are cheap, and they
don't look terrible. Recent evidence suggests
that although plants require mostly red and blue
light, ANY light, in high concentration must be
applied for the plants to open their stomata
thus permitting respiration. This goes a long
way toward explaining why some people are able
to grow beautiful aquarium plants with just cool
white and warm white tubes. Enough light, of any
type will grow plants. These tubes are far from
optimal however and they really are almost
completely devoid of the necessary red and blue
portion of the spectrum. If you can grow decent
plants under these lights, you will do even
better under more appropriate lights. These
tubes are available anywhere fluorescent tubes
are sold and are the cheapest tubes available,
figure in 1990 US dollars these tubes cost
between $1 and $2.
Daylight
Daylight tubes are the next big improvement in
more natural, (that is a more closer
approximation of sunlight) fluorescent tubes as
a result of an improved phosphor formulation.
Although daylight tubes output a spectra that
although does not fully emulate sunlight, it is
significantly better than earlier cool white and
warm white tubes. These tubes are occasionally
available at hardware and department stores.
They are not uncommon and any lighting supplier
should have them or be able to order them. They
cost a bit more than cool white, but are not
expensive. Figure about $3 to $4.
Plant growth lights
Epitomized by the Sylvania Gro-Lux (tm) tube,
plant growth lights are, unlike all other
fluorescent tubes, meant solely for promoting
plant growth; you won't find these illuminating
somebody's home or office - with one exception.
Where I work, a receptionist thought it would be
nice to have pink lighting in the lobby and
ordered and had installed some plant growth
tubes. You do get used to it, but they are most
disconcerting when initially encountered.
GE's
version of this tube is called "Gro- Sho", other
plant growth tubes that are available are these
tubes relabelled for specialty pet/aquarium
companies. Gro-Lux type tubes have an output
spectra with two large spikes. One in the blue,
and one in the red portion of the spectra. There
is almost no light emitted in any other portion
of the spectra and as such, they cast an eerie
purplish glow, and do not appear very bright.
The spikes in the red and blue occur quite
abruptly and are quite steep. This spectra was
chosen as it matched the absorption of visible
light by chlorophyll in a test tube. In the 50's
a study was conducted on various lighting types
and phosphor formulation on plant growth, the
results of which were published in the book
"Lighting for Optimal Plant Growth" (Kent State
Press) The phosphor formulation of Gro-Lux type
tubes was improved upon. Instead of two steep
abrupt spikes in the red and blue, there are two
slow rising large "bumps"; the peaks in the red
and blue were not as high, nor did they rise as
sharply. Instead of concentrating all the energy
in these two narrow energy bands, the output was
tuned to a wider output spectra still however,
centered around red and blue. It became
commercially available from Sylvania as Gro-Lux
Wide Spectrum; GE named theirs Gro- Sho Wide
Spectrum. These are more pinkish than purple and
are indeed what is in the lobby of the building
where I work.
Incidentally,
you could never get away with regular Gro-Lux
(as opposed to Gro-Lux wide spectrum) tubes in a
lobby; they look dark, don't illuminate well and
are a very deep purple. The Wide spectrum plant
lights are brighter and don't look like a 60's
psychedelic poster shop when used to illuminate
a room like a regular Gro-Lux would. Philips
makes a plant light they named "Agro-Lite",
which is a minor variant of the wide spectrum
Gro-Lux. They commissioned a study at a major
American university comparing their Agro-Lite to
wide spectrum plant lights. The Philips tube
resulted in 2 - 10% greater growth in a variety
of terrestrial food crops when compared to other
wide spectrum plant lights.
Since
these tubes are quite commonly used for (non
aquatic) houseplants they are reasonably common
in hardware stores or nurseries, although what
typically happens is a store will only sell one
vendors fluorescent tubes. Even worse, they
don't recognize the difference between plant
lights and wide spectrum plant lights with the
result being you will usually find plant lights
or wide spectrum plant lights from one
manufacturer in a store. Wide spectrum tubes are
reasonably inexpensive, although regular Gro-Lux
type tubes tend to be a bit more expensive still
- the chemical that makes up the phosphor which
produces red is the expensive part. In a pet
shop these can be between $10 and $20. From a
lighting supplier a Gro-Lux tube is about $9
while a wide spectrum tube is about $7.
Full Spectrum
Full spectrum tubes imitate, as closely as
possible, natural sunlight by emitting light in
every spectral range. All the different colors
of visible light and a very small amount of
ultraviolet is emitted. The Duro-Test Company
produces "Vita-Lite" tubes. GE produces "Chroma
50", Philips produces "Colortone 50", Sylvania
produces "Designer 5000K". All these tubes have
an output spectrum that is similar to sunlight -
about as close as modern chemistry can bring us.
These tubes try to imitate equatorial sunlight
at noon, which has a color temperature of around
5000K.
Noonday
sunlight from northern climes has a larger
amount of blue in the spectrum, as has a color
temperature of 7500 Kelvin. Since the red
pigment in plants is limited by blue light these
are sometimes useful. Duro- Test sells a "Vita
Lite 75", GE sells a "Chroma 75" and Philips
sells a "Colortone 75".
There
is quite a disparity in availability and price
of these tubes. The Vita Lites have very good
distribution. They can be found in most aquarium
stores (and many pet stores as they are also
used for illuminating lizards who need the
Vitamin D from the ultraviolet light). The
downside of this is like anything you buy in a
pet store that you can buy in a hardware store,
they price can be quite high when buying them
from a pet store: $15 - 20+. The same Vita-Lite
tube from a lighting supplier is about $7, and
the Chroma 75 I have obtained for less than $5.
They are nearly identical.
Tri-Phosphor
Philips makes the most popular range of T12
tri-phosphor tubes, the "Ultralume" series.
Recognizing that the primary light colors are
red, green and blue, Philips made a tube that
fluoresces very sharply only in these three
narrow wavelengths. The light emitted appears
white, and very bright. They are used primarily
in clothing stores because they completely lack
emitted ultra-violet, which bleaches clothes.
Ultralumes come in color temperatures of 3000,
3500, 4000, 4500, and 5000 which is accomplished
by varying the amounts of red, green and blue
phosphors. Since red is the most difficult color
light to obtain from fluorescent tubes and the
Ultralume 35 has the most red, this is probably
the most interesting tube from our perspective.
Ultralumes are in the $7 range and can be found
at better pet/aquarium stores. Philips tubes
seem to be difficult to find in some areas,
notably the West coast although I have
occasionally seen Ultralumes on sale in
department stores there. Again, a lighting
supplier can usually get any of these tubes.
Actinic
These tubes emit light only from the blue end of
the spectrum and are used in marine setups to
supply the blue that is missing from normal
aquarium lighting but is required by marine
algae, anemones and corals. They are usually
only available from specialty aquarium stores
and are not cheap. They have little or no
application for growing freshwater aquarium
plants.
Reflector and
Aperture
Of the large manufacturers of fluorescent tubes,
only Sylvania makes reflector and aperture
tubes. Many of the new aquarium specific tubes
have reflectors, but have little data to back up
their assertion that the reflector is worth the
extra cost. Sylvania however, has a data sheet
on their reflector and aperture tubes.
Quoting from the "Sylvania Engineering
Bulletin O-338"
"Aperture and reflector fluorescent lamps
differ from standard fluorescent lamps in that
they allow a certain amount of control over the
direction in which the light is being sent. As
sketched in Figure 1, a reflective coating is
placed between the outer glass and the phosphor
coating. This reflective coating provides the
direction control by reflecting most of the
incident light and directing it through the
uncoated surface or clear window of the aperture
lamp."
"The
total light output of reflector lamps is
actually less than that of standard lamps. These
lamps are intended for applications which can
best utilize their special light distribution.
The light is often too bright for direct
illumination, but when used with reflectors it
can be a very effective means of controlling the
light."
Reflector tubes have a reflective coating
covering 235 (or 135) degrees of the interior.
Over that, they have a phosphor covering the
entire inside of the bulb.
Reflector
lamps are available with a 235 degree or 135
degree internal reflector.
They
are available in a number of sizes in Cool
White, while one is available in Gro-Lux in a
R/GRO/VHO 215 Watt 96" lamp. Aperture lamps have
a 330 or 300 degree reflective coating. They
have a phosphor coating covering 330 or 300
degrees of the lamp. There is a 30 or 60 degree
clear glass opening or "aperture".
"The aperture lamp has a lower light
output that standard fluorescent lamps, because
some of the phosphor, which converts ultra
violet to visible light, has been removed. But
when these lamps are used with reflectors or
lenses, they provide a very concentrated beam,
closely projected in one direction. This allows
more light to be delivered to a small area.
"Applications
of the lamp are bridge lighting from the rails,
aircraft landing strips, highways and approach
ramps, billboards and sign lighting, sport areas
and marina lighting."
The aperture lamps are only available in 3
models: 4 foot 30 degree aperture cool white, 4
foot 60 degree cool white, and 8 foot HO 30
degree cool white.
Special purpose
Beginning in 1990, specialty aquarium supply
companies began selling fluorescent tubes aimed
specifically for the aquarium market. These
tubes are sold primarily for the marine trade,
as corals and anemones have even more exacting
requirements than freshwater aquarium plants.
The first to be introduced was the Triton tube
made by Thorn/EMI for Interpet (who were in turn
bought by GE in 1990) tube from England. These
are essentially a tri-phosphor design but give
off a pinkish light reminiscent of wide spectrum
plant lights. The output spectra looks like a
Gro-Lux with an additional green spike. The
amount of light they give off is quite
substantial - but so is the price. They start in
the $15-$20 range and go up. Essentially a
"super Gro-Lux" the Triton tube was significant
in that it was the first fluorescent tube
designed specifically for aquarium use. It is
also significant in another respect. The
manufacturer claims the spectral output of the
tube degrades less than 10% over 7000 hours, a
time period in which a Gro-Lux type tube will
have lost about 60 % of it's light output. Also,
unlike a regular fluorescent tube, a triton will
just refuse to start or light up when it's life
has expired (about 2 years). These features are
meant to address the cathode decay problem and
eliminate the need to change tubes.
It
did not take long, however until other small
manufacturers jumped on the specialty
fluorescent tube bandwagon. Looking at the
January 1991 Freshwater and Marine Aquarium
magazine, there are no less than 5 different
specialty fluorescent tubes advertised. There is
the "Actinic Day" tube which is a white tube
with a fair amount of actinic (blue, in the
range of 380 - 480 nanometres) light as well. An
ad for the Actinic Day tubes compares the graph
of their spectral output to that of the Triton
tube, with naturally, the actinic day tube
showing a more intense spectrum. A few pages
later is an ad for "Tritinic" brand tubes that
are similar in design - tri-phosphor white with
a good deal of actinic thrown in, and lo and
behold is a graph comparing them to Actinic Day
tubes, with of course the Tritinic tube having a
yet more intense output spectra. Competition for
your fluorescent tube dollar is fierce; it's a
bloodbath out there.
The
superwhite/actinic tubes have a built in 180
degree reflector, which is simply a piece of
metal insides the tube that covers the top of
the tube so that all the light escapes directly
out from the bottom half of the tube. This is
not a new trick, some industrial tubes (such as
8 foot VHO Gro-Lux) do this, but this is first
tube for home use to employ such a device.
These
tubes are made in small quantities for aquarium
hobbyists and priced accordingly. They are only
available from aquarium retailers and each cost
$15+.
There
is a specialty tube that is not a recent
introduction nor is it made for home aquaria.
Sylvania makes a "fluorescent incandescent" that
emits light much as an incandescent bulb does -
mostly red and near red. They are almost never
stocked, and are not cheap, about $10 US.
HO/VHO
HO refers to High Output, and VHO is Very High
Output. These tubes output more (and a lot more)
light by drawing more (and a lot more) current.
They are more expensive tubes to buy, require
larger more expensive ballasts and don't last as
long. The conventional wisdom in the aquarium
trade about these tubes is that if you need a
lot of light then it's okay to use an HO, but
the VHO's are more bother than they're worth.
Neither last as long as regular tubes. A ballast
for an 8 foot VHO tube is an enormous black box
that draws a lot of current, and gets very hot.
Even the tubes themselves get hot. If you need
this much light you should probably be thinking
about HID lamps. HO and VHO tubes come in many
sizes and types, such as cool white, warm white,
daylight.
Gro-Lux and Gro-Lux
wide spectrum
Longevity
Standard T12 four foot fluorescent tubes have
about a 10,000 hour lifespan, but as stated
earlier, their usable life is much shorted
because of decreased light output over time. All
other tubes are less (by about half) than this,
but again, it's a moot point as they should be
replaced every six months.
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.
Trade-offs
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 vapor 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 vapor, sodium vapor and metal halide.
Mercury vapor
When you see a bright light illuminating some
industrial building and it has a decided bluish
cast - that's mercury vapor. Mercury vapor 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
vapor 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 vapor 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 vapor 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 haven't as yet gained
great acceptance with aquatic gardeners.
Metal halide
Like sodium vapor, these lamps come in two
versions, regular and color 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 vapor,
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 color temperature bulb. You have to go to
a 250 watt bulb to get 5400K color 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 esthetic 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 color
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 color 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
vapor or sodium vapor 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 vapor lamps, but have never
heard of any success with them. People have had
some mixed success with mercury vapor 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. |