Grunff wrote:
G&M wrote:

The time is actually programmed in by the manufacturer. Most now use the
STMicroelectronics chip and it is easy to set this from 1 second to days.
The slower it turns on the longer the tube will last.


Well I'll be... I always wondered why they took so long to warm up;
never realised it was ramped!

Why does it affect longevity? I thought the only faliure modes were
driver failure and phosphor ageing.

You get the best life from a bulb if you turn the heater filliments on
some 1-2 seconds before actually starting the light.
If you don't, then the heaters get bombarded with ions and this dislodges
lots of their substance, which ends up on the walls of the tube.
With a tube that's working properly, the heater emits electrons, which
neutralise the ions before they get to the fillimnent.

The actual bit of the heater which does the work is in fact heated a bit
by the incoming ions reacting with nearby electrons, so runs a bit hotter
than due to the current alone.

Similarly with CCFLs, the unheated cathode actually gets hot, which does
similar things.
Both of these are a reason why dimming some fluorescant tubes may cause
blackening at the ends of the tubes and premature failure.