Karl, I love that sayin', wish my wife understood it a little better.
(to Stephen)
However when it comes to temp control its varies a lot, and mostly because of the user.
I say that because each type of control can be matched with a type of user, and the heat element, in my case heat tape.
For example, every cage I have now is run off a dimmer or rheostat. This type of control is cheap and depending on your setup mildly easy to use. Modern dimmers are essentially a voltage on/off type system they turn on and off dozens of times a minute, all to keep the output at an equal level.
The benifit of the dimmer is the they are cheap enough that you can equip every cage in a rack orevery cage in a setup fast. Also you can turn off un used cages or racks so there is no wasted energy heating an empty cage.
The draw backs are as the room heats up the cages heat up so there is no upper limit. This means the room has to be very stable or the user must monitor the cages very often. Even in a stable room minor adjustments will have to be made daily no matter what. Another down fall is that its hard to tell if its on or off, there is no light to indicate function. Lastly old dimmers when they lost power reset themselves to full open, this is not the case with modern dimmers.
On/Off T-Stats are identical to Dimmers, except they are based off temperature via a probe rather than the current flowing through them. The benifit here is for a user that doesn't have the time everyday to check and adjust each cage. While more expensive than dimmers they can be used for blocks of cages. However only the cage in which the probe is placed will match the settings, cages on the floor or those against the ceiling will see minor changes either cooler or hotter than the mean setting. Ususally in the case where an entire rack or stack of cages is run off a one T-Stat, its better to place the thermostat probe in the middle.
The disadvantages to an on/off T-stat is that the constant on-off cyle causes colling and heating cycels within the cages. By the time the probe cools and turns the unit back on it may be some time for the element to respond heat up and rais ethe temps. Conversly when the element drives the temps high enough for the probe to turn the unit off, it may be some time before the element cools and the temp begins to fall. This cycel effect can be hard to adjust, and can be hard on the element particularly lighting. Lastly some cheaper units are known to fail in the on position and the run away voltage can bake the animal.
Proportional T-Stats are the last option on the list. They provide a constant current to the element, virtually eliminating the cycle effect. To do this as teh probe senses the temperature drawing close to the high, it loweres the voltage so the elemnt doesn't heat up as much. Conversly as the temps approach the lower limit the probe increases the voltage to the element so the temp doesn't fall below. It still has a cycle effect but the fact the element never switches off means there will never be exostensially cooling do to the element warming up. It also narrows the cycle to within a few degrees of the mean.
The disadvantages are cost ery expensive and some of the cheaper models are know to fail, but the failure doesn't cause runaway heating, just none at all. Which with some species could mean death just the same.
There are newer units like the Herpstat Pro that have 4 probes so the single unit that can control 4 cages. And On/Off T stats like certain Ranco models can be outfitted with 2 probes to control the limits to heating a cooling cycles.
If I was you I wouldn't worry about a T-Stat for a light bulb, any model will cause un needed strss on the filiment. The best bet would be a dimmer. Or use a ceramic emitter like Karl suggested.
As far as probe placement, you don't need to place teh probe at the bottom. However you will need to use a temp sensor like a heat gun to adjust the unit. By this I mean if you place the probe at the top of the enclosure and it reads XXX and the desired temp at the bottom is YYY. You will need to change the mean temp on the unit so that the temperature at the bottom achieves your desired ZZZ temp. You just can't use the displaied temp on the unit as teh actual temp.
For example in a rack if I place the probe next to the tub on the heat element in may read 90°F, but inside the tub it may read 88° if my desired temp inside teh cage is 90° I will have to increase teh temp on the unit to 92° to allow for the change.
Probably more info than you need but I was on a break.
Cheers
-----
Jeremy
"I am become death, the destroyer of worlds" July 16, 1945 Robert Oppenheimer
0.1 Snow "Khal" RTB
1.1 Double Het "Sharp" Snow RTB's
1.0 Hypomelenistic RTB's
0.2 Pastel Hypo RTB's
0.1 Suriname RTB
0.1 Anerthrystic RTB
3.1 Red Bearded Dragon's
1.0 Ball Python
1.1 Cream Golden Retrieviers
1.0 Pomeriaian
0.3 Catus Terribilis
0.1 Spouse
1.0.1 Child
