The Orchid House
Indoor Plant Lighting
There are a number of different approaches used for growing
plants under lights. 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
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
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". Plants, in general, absorb red and blue light and
reflect green light. Our eyes are most sensitive to the color
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 absorption of all other colours, or wavelengths of
light, by the atmosphere.
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
colour can be measured in degrees Kelvin (K) and the colour
rendering index of a light source can be measured and expressed
as CRI. (0 degrees Celsius = 273 degrees Kelvin; 0 degrees Kelvin
= absolute zero)
Colour temperature - degrees Kelvin
White light can have different "warmths". A bit more red/yellow
makes white light appear "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 of 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
Colour rendering index (CRI)
The colour rendering index identifies the degree of colour shift
objects undergo when illuminated by a particular light source
compared to a standard 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.
The color rendering is important when examining flowers under
different light. Because cool white (blue) fluorescent lights
lack red, red flowers look dull, almost grayish. Sodium or
mercury lights are even worse for distorting color.
A light meter may be used to measure the amount of light,
measured in foot-candles, emitted by a light source, measured at
some distance from the source. Growing information for a plant
will give an indication of the amount of light the plant
requires, usually stated in foot candles at the surface of the
Light meters for use in photography are designed to be
sensitive to the same wavelengths as the human eye. That is not
what a plant sees! To measure correctly what a plant sees, you
must use a meter that provides a measure of photosynthetically
active radiation (PAR), the wavelengths of light most important
for plant health. These wavelengths, between 400 and 700
nanometers, are critical for the photosynthesis and chlorophyll
production that drive plant growth. (A nanometer is one billionth
of a meter.)
Good light, free, but hard to control
This is of course what plants are used to and it can hardly be
argued that this is anything less than the most natural. However
coaxing enough sunlight onto your plants throughout the whole
year from the top rather than from the side as through a window
can be problematical.
Sunlight is the certainly the cheapest way to illuminate your
plants, although it is unreliable and very difficult to regulate.
This is subject to geographical variation, of course. If you live
in California and have a skylight over a plant stand, you might
be getting enough light. If however you live in an area that does
not get a lot of sunlight or your plants are stacked in rows in a
basement, you will obviously need supplemental 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
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. 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 bulb's outer casing and although it
is still plenty hot, it is not as hot as 200 degrees Celsius.
Output spectrum 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 spectrum 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 spectrum.
The great disadvantage to incandescent lights is their
inefficiency - you don't get a lot of light compared with how
much energy you 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. [No longer. They are being phased out in favor of more efficient sources.]
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
grower 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 growers 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.
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
Guinness book of world records lists the longest lasting light
bulb as being an incandescent bulb in a firehouse 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
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 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 spectrum or colour of the emitted
light. (Fluoresce has nothing to do with flour.)
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
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.
[The older T12 linear fluorescent lamp types are being phased out in favor of
newer, more energy efficient fluorescent systems like T8 and T5, and CFL.
This tube has a diameter
of 1.5 inches and is available in 18", 24" 36", 48", 72" and 96"
lengths. T12 tubes are available in HO (High Output) or VHO (Very
High Output) which draw more and much more current respectively,
but produce more light than regular T12 tubes. 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. The T8 or
"slimline" fluorescent has a 1" diameter tube and is available in
24", 36" and 48" lengths. 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 phosphor chemistry is what makes the difference between a
cool white and a daylight tube and every tube is available with a
dizzying array of choices in this area. As the composition of the
phosphor changes so does the spectrum of the visible light being
emitted by the tube.
For illumination for plant growth 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
Use Four Foot Tubes
Although fluorescent tubes come in many sizes, volume of scale
dictates that there is really only one size - the 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. 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.
In North America the "Big Three" in fluorescent tube
General Electric (GE)
They all make, almost without exception, the same tubes, under
different trade names although there are some notable exceptions.
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"
If all you want to do is illuminate your plants 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 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.
Daylight tubes are the next big improvement in more natural light
(that is a more closer approximation of sunlight) as a result of
an improved phosphor formulation. Although daylight tubes output
a spectrum 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.
Plant Growth Lights
Epitomized by the Sylvania Gro-Lux® 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.
GE's version of this tube is called "Gro-N-Sho". Gro-Lux type
tubes have an output spectrum with two large spikes, one in the
blue, and one in the red portion of the spectrum. There is almost
no light emitted in any other portion of the spectrum 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 spectrum 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
formulations 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 produce wider bands still
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.
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 houseplants they
are reasonably common in hardware stores or nurseries, although
what typically happens is a store will only sell one vendor's
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 tubes imitate natural sunlight as closely as
possible 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.
Noon-day sunlight from northern climes has a larger amount of
blue in the spectrum, having 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, the
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
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.
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 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
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. 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
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.
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 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
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.
LED Replacements for Tubes
You will find that T12 tubes have pretty well left the marketplace and T5 and T8 tubes are not far behind.
What's the difference
However manufacturers are producing replacement tubes using LEDs. They are more efficient, producing less heat.
If you have older fixtures and would sooner not replace them, look for replacement LED tubes.
You should consider that if the ballast fails, you will need a new fixture.
For information on T12 replacements
Pretty much is also the same for replacing the newer T5 and T8 fluorescent tubes.
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
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
growers who need lots of light.
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.
There are three basic types of HID lamps: mercury vapour, sodium
vapour and metal halide.
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 spectrum that is almost entirely
blue-white, with very little red. Worse, the spectrum 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.
These lamps have a duo-spectrum for colors, besides it emitting
light on the blue/white end of the spectrum, it does emit reddish/yellow
light (from the filaments), therefore, it does have more of a light
spectrum that plants depend on. 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
these bulbs are expensive, around $50 for 250 watts.
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 are
generally used in conjunction with sunlight or metal halide
lights. 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
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 grower 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
area you are trying to illuminate.
Many small plantstands 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 can be an excessive amount of heat being given
off from the bulbs.
Incandescent illumination, although inexpensive in initial
setup cost is not recommended. The heat generated by these light
bulbs almost always overheats the plants. The cost to operate is
fairly high, and the quantity of light is low compared to the
amount of heat produced. 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 could be used 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
your plants 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
that has an incandescent fixture the new compact fluorescent
bulbs with integrated ballasts will, in many cases, screw right
into the existing socket. 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
Low light plants will do ok under two Gro-Lux or Gro-Lux wide
For growing high light plants, two (or four, depending on
preferences) chroma 75's can be used. Or an HID lamp would
probably be the most appropriate. Rather than a large number of
fluorescent tubes to supply enough light, 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
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 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.
Modern LED fixtures are replacing most of the other options when it comes to lighting plants.
This article was adapted from an article on aquarium lighting
by Richard J. Sexton.
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