Subject: Indoor Plant Lighting
From: [email-masked] (Richard J. Sexton)
Date: Sat, 9 Jul 1994 05:10:20 GMT
Newsgroups: sci.aquaria,alt.aquaria,rec.aquaria,alt.aquaria.killies,bionet.plants,rec.arts.bonsai,alt.drugs,rec.gardens.orchids,rec.gardens

[I think I've managed to hit every usenet group that grows stuff]

This article, although primarily aimed at growing aquarium plants
is applicable to growing anything.

==================================================

TYPES OF LIGHTS

     o 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, colour 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 COLOUR

     o 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.

     o White light is all colors

When we see a rainbow, we are seeing white light split up into it's
component colours, hence the expression "all the colours of the rainbow". 

     o Sunlight is different in different places in the world

Sunlight contains, more or less, equal portions of all colours of sunlight.
Northern sunlight, that is, sunlight in areas north of the fortieth parallel,
has more blue than equatorial sunlight because of absorbtion of all other
colours, or wavelengths of light, by the atmosphere.

     o 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.

     o How is light measured ?

Light quality is expressed and measured in many ways. Light colour can be
measured in degrees Kelvin (K) and the colour rendering index of a light
source can be measured and expressed as CRI.

     o Colour temperature - degrees K

White light can have different "warmths". 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 colour temperature, given
in degrees Kelvin. Think of colour temperature as the colour 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 blueish tone. Sunlight is somewhere around 5000 degrees Kelvin.

     o Colour rendering index (CRI)

The colour rendering index identifies the degree of colour 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
colour 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 colour 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 vapour lamps have very low CRI's.

NATURAL SUNLIGHT

     o 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
litre 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

     o 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.

     o 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 vapour. 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.

     o 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 colour temperature of
2700K, while halogen bulbs have a colour 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. 

     o 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 yuppie 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.

     o 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.

FLUORESCENT LIGHTING

    o 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.

    o 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 vapour. When energized, the mercury vapour 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 colour of the emitted light.

    o 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 vapour. 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.

    o 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.

    o 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. 

    o 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.

    o 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.

    o 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.  

    o 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-N-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 absorbtion 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-N-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.

    o Full Spectrum

Full spectrum tubes imitate, as closely as possible, natural sunlight  by
emitting light in every spectral range. All the different colours 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 colour temperature of around 5000K.

Noonday sunlight from northern climes has a larger amount of blue in the
spectrum, as has a colour 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.

    o Tri-Phosphor

Philips makes the most popular range of T12 tri-phosphor tubes, the
"Ultralume" series. Recognizing that the primary light colours 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
colour 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 colour 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.

    o 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.

    o 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.

    o 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 triphosphor 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 - triphosphor 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.

     o 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

     o 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

     o 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.

     o 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.

        o Types

There are three basic types of HID lamps: mercury vapour, sodium
vapour and metal halide.

     o 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.

     o 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.

     o 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.

     o 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.

     o 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.

-- 

Richard J. Sexton                         [email-masked]