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 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.
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.
