You are actually right on in your thinking. The full ON then OFF (where the filament cools considerably before going ON again) does affect filament life. So much depends on the cage setup though that it is very hard to make generalizations.



One generalization that can be made is this: An insulated cage does alot for extending bulb life compared to having an open screen top. This holds true no matter what temp controller you use.



All things being equal (meaning cage setup and bulb) using a proportional controller will result in less energy used and longer bulb life compared to an ON/OFF controller. The million dollar question is how much. Very hard to say, but I would guess much less than 10% savings. So for a few bulbs, it is minimal effect on your wallet. If you had 1000 bulbs, then you could argue the cost savings.



As far as performance, proportional is best for holding a more constant temperature.



Your dimmer idea in-line with an ON/OFF controller is good when the bulb wattage is higher than you would like, or as a fail safe overtemp limit. The ON/OFF controller must use a relay for this to work. If it uses a solid-state device instead of a relay, forget it. For the relay type (most are, because relays are cheap), at very low settings of the dimmer, the heater, once switched OFF, will likley not come back on until the dimmer is turned up a bit. That is an effect of the semiconductor trigger in the dimmer not having enough voltage once the ON/OFF controller switches it OFF. Not usually a problem if you keep the dimmer above 40-50% power, which is well within what you will do anyway.



When you put a dimmer in-line with an ON/OFF controller, put the dimmer bewteen the controller and the heater. You want the controller to turn power ON and OFF to the dimmer. The other way (ON/OFF controller between dimmer and heater) will work too but has no advantage and in fact has the disadvantage of not being able to feed multiple dimmers with a single ON/OFF controller.
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Mark

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