Terrarium Lighting 101
Anyone popping into this messageboard will undoubtedly see many questions
asking about lighting their terrariums so I decided that perhaps a quick
introduction to the topic might be in order for newbies to check out and get
a general idea of what is necessary to grow plants with artificial light.
LIGHTING A TERRARIUM
It is important to use a cover over your terrarium. Whether the lid is
plastic, plexiglass or all glass with a rubber hinge in the middle it will
protect your plants from the drying heat generated by the lighting fixtures.
The lid will also keep the humidity in with the plants-where you want it. Do
not use plastic aquarium hoods that are deigned as a one piece with light
strip or screw in bulb. This is not enough light to grow plants.
Most new collectors will be using a premade fishtank converted to terrarium.
If you are using fluorescent tubes you should put AS MANY tubes over the tank
as is possible. Over a 12” wide tank (measuring from front glass to back
glass) you can easily fit 4 tubes (2 twin tub strips), over an 18” wide tank
you can fit 6 tubes, a 24” wide tank can have 8 tubes and so on (apx 2
tubes/one twin strip light per 6” of tank depth will give an intense yet
cool burning light which will make your CPs very happy).
It is also a wise idea to cover all side glass surfaces of the terrarium with
tinfoil, mylar, mirror or some other reflective material so that none of the
light is lost and it bounces around inside the terrarium infinitely. You can
tape only the top of the front flap so that you can lift it to view your
plants anytime and replace it when you're done looking so that your plants
will receive every beneficial lumen they can. The difference is immediately
obvious as one is taping the first few sheets of reflective material onto the
tank as leaves once slightly shadowed suddenly become several shades lighter
and it will be more so as new pitchers open and develop truly stunning
When your collection (or fanaticism) has grown into the stage where you
construct a large growing chamber you may need to switch to power compact
flourescents or metal halides to effectively light the entire chamber. Using
these high intensity forms of lighting and larger growing chambers will
necessitate some form of humidity and temperature control (especially for
highland Nepenthes) so everything stays in balance environmentally.
Now the Bulbs...
Artificial lighting is usually packaged with some information on the carton
detailing the qualities of the particular bulb you are about to purchase.
However, this information is useless to the hobbyist if they do not know what
Hopefully this section will help you to understand why one bulb of the same
wattage may be less suitable for your plants than another.
COLOR RATING INDEX
The Color Rating Index or “CRI” of a light bulb indicates the closeness the
bulb comes to imitating the sun. The suns CRI is 100, bulbs rated from 75-100
are suitable, 90-100 are best for simulating true “white” sunlight color.
KELVIN RATING or “COLOR TEMPERATURE”
The Kelvin rating, or “K” of a bulb determines the yellow to bluish tint of
the bulb. The suns Kelvin rating varies depending upon the latitude and
angle of the sun towards the earth.
The noonday sun in the tropical zones near the equator have a Kelvin rating
of 5000-5500K and the color is slightly “golden” (or “yellow/green”).
Whereas the noonday sun in Chicago Illinois is 6500K and is slightly “blue”
and Anchorage Alaska more towards 7100K which is even more “blue.” On the
far end of the spectrum a novelty “blacklight” is approximately
30,000-40,000K. A word of warning, using a blacklight on a CP terrarium is
essentially useless unless you wish to use it for night viewing to simulate
the moon which, by the way, is not necessary for successful cultivation but
is a fun experiment. A “soft white” or “warm white” bulb is usually around
3200K which is far too dull and yellow to be effective for photosynthesis in
the plants tissues.
WATTS V.S. LUMENS
Lumens is the value which should be paid most attention to when shopping for
a bulb. Lumens is a means of measuring light intensity and tells you how much
actual light will be output from the bulb. The wattage of a bulb simply tells
you how much electrical power it takes to run the bulb and is NOT a very good
indicator of how suitable the bulb is for plant growth. Usually the higher a
bulbs wattage, the higher the lumens (light output) but this is not always
so. If you compare a 40 watt screw in incandescent bulb and a 40 watt
fluorescent tube you will be getting almost 10 times the lumens from the
fluorescent tube than you will from the incandescent. Also, with expanding
technology in regards to artificial lighting such as the screw in Compact
Flourescents (often referred to as the “5 year bulb”) these put out more
light while using less electricity.
You must also remember that the further a plant is from the light the fewer
lumens will reach it and the less chances the plant will receive maximum
color spectrum (CRI) from the light the red spectrum is lost first followed
by orange, yellow green and finally blue. So while a single fluorescent Bulb
of 3200 lumens/40 watts sounds pretty good you have to remember this value
reading is taken on the bulbs surface, the number of lumens drops
considerably the farther the bulb gets from the surface, not to mention being
separated from the plants via plastic or glass on the required terrarium lid.
Thus, more bulbs are needed to be combined together help to “punch” the
light down farther to evenly illuminate all of your terrarium or growing
FORMS OF ARTIFICIAL LIGHTING
FLUORESCENT STRIP LIGHTS
By far the most easily accessible form of artificial lighting for your CP
collection is the twin tube strip light. Twin tube strip lighting kits may be
purchased for as little as $5 - $20 at most home improvement centers. The
bulbs for these units are usually available in a wide range of color
temperatures to the observant buyer. Ideally a bulb color temperature of
5000-5500K and with a color rating index of 90-100 simulates tropical sun
almost exactly. GE makes such a bulb called Chroma 50 (marketed as “Sunshine”
in an orange & yellow sleeve) but they are more expensive and when using
only these bulbs one gets the feeling that the light is very “golden green”
or “yellow/green” which may be bothersome to some people. So using a bulb or
two called “cool white” or “daylight” with a color temp of 6500K-7100K to
add some blue spectrum and balance out the color to the human eye and not
affect the plants too much.
POWER COMPACT / COMPACT FLUORESCENT / JL LIGHTING
This is a relatively new form of fluorescent lighting which effectively
quadruples the output of normal flourescents in approximately 1/2 the space.
These work best for odd shaped terrariums (such as octagonal or hexagonal)
which cannot have standard fluorescent tubes placed above them due to their
unusual lengths/widths. They also work well for lighting deeper/taller
terrariums because they have 2-4 times the lumen output of standard
fluorescent tubes in a smaller bulb. A variety of lighting units, wattage's,
color temps and bulb sizes (from 6” to 47”) can be obtained from saltwater &
marine aquarium suppliers. NOTE: These bulbs cannot be used in the standard
fluorescent fixtures, a special ballast must be obtained, making their cost
SCREW-IN COMPACT FLOURESCENTS FOR INCANDESCENT FIXTURES
These bulbs are also relatively new (often sold as “5 year bulbs”) but until
now they have been only available as “soft white” which is unsuitable as a
plant light. However several companies have begun making the screw-in bulbs
in daylight 6500K color temp which are perfectly suitable for smaller
terraria. They are available at large hardware stores from 15 watts (1100
lumens) to 65 watts (8000 lumens) in power. These are very good bulbs but
they do cost more than traditional fluorescent lighting.
METAL HALIDE / MERCURY VAPOR / HIGH PRESSURE SODIUM / HIGH INTENSITY
These are far more advanced (and expensive) forms of lighting. Suitable
mainly to experienced hobbyists growing a large room size collection or as
supplemental lighting for greenhouses on the dark days of a gloomy northern
hemisphere winter season. Not for use on terrariums under 4' x 4' x 4.' These
forms of lighting come in wattage's ranging from 175 watts to 1000 watts. The
ballast's and bulbs both generate a great deal of heat along with the light
so temperature and humidity in an enclosed space such as a large
terrarium/grow area must be closely controlled when using these forms of
lighting so the plants are not scorched or cooked. Plants must be placed
approximately 24-36” from these types of lighting units. When using these
types of lights for a large terrraium/grow closet, etc. you will also need to
buy the following: timers, fans, humidistat and thermostat (two stage
thermostat if you are growing highlands and need to cool the room at night).
As with the Power Compacts a variety of high intensity lighting in various
wattage's and color temps may be obtained from saltwater aquarium dealers.
I should also add that when firing up a few metal halides may get you a visit
from your neighborhood DEA (Drug Enforcement Agency) due to the spike in
power usage, so long as you're just growing CPs you don't have anything to
worry about, but you should be aware of the possible knock on the door!
I hope this little article will give you some place to start when seting up a
terrraium. Light is the #1 necessity of your precious plants - please do not
skimp on it!
-Josh Cook /Swords"