Energy saving lamps

Basically, the operating temperature of the linear tube - I assume you mean 5' - is much closer to room temperature. With CF, they run at 100C or so. In order to get the optimum pressure of mercury when running, the 'off' pressure is rather lower.

It's also a compromise between electrode life and turn-on speed. If it takes 1-2 s to start, then it allows the electrodes to warm up before the tube is started.

This causes less wear of the electrodes and blackening at the ends than 'instant on'. (this is completely seperate from the tubes taking time to warm up once on)

Sorry I meant 5', when you say they run at 100C I take it you don't mean the operating temperature as I have just touched the tube of a 15 watt CF and it is warm but definitely not 100C Trevor Smith

The message from Ian Stirling contains these words:

Doesn't it also increase the output per unit area? A more important consideration in CFLs than in linear units.

Actually, it's not. Initial output is nearer the final brightness than is the case with compact fluorescents, but long linear tubes still have a run-up time, and it's actually much longer than a compact fluorescent (20 minutes is quite typical).

Conversely, long linear tubes are designed to run at 40C in a ambient of 25C. (Actually, that's T12 tubes -- I don't have the figure for T8 tubes, but it's probably not a lot higher.)

Another factor is that most compact fluorescent tubes use a mercury amalgam pellet to control the mercury vapour pressure over the range of operating temperatures the tube might find itself in. It takes time for this pellet to warm up and for the mercury to diffuse out of it. This is not necessary in T12 and most T8 tubes, although all the new T5HE and T5HO linear tubes use it.

It will depend on the enclosure, but they are designed to run with the tube up to 100C.