Every room in this house, other than kitchen and bathrooms has a dimmer. I can't recall the last time one failed, and we've lived here
18 years.(Oh, I tell a lie; I had to replace one in the sitting room because I Superglued it's knob back on a bit enthusiastically and glued the whole thing into one immovable lump.)
I haven't had one fail, but...
I fitted one to a son's bedroom light. It wasn't an expensive one, but not exactly cheap either. I found that bulbs were lasting 7-10 days....went back to a switch, bulbs then OK. Put an MK dimmer on. No further trouble.
Anyone else come across this failure mode?
Ahh - yellowy lights and candles arent my thing :)
NT
It doesn't make much sense. A filament bulb will fail early due to excess voltage, heat or vibration, and I don't see how a dimmer can contribute to any of these - quite the reverse. A dimmer even when full on has an 'insertion loss' which slightly under-runs the bulb and should if anything increase its life.
Yep.
Generally the MK ones have soft start. This seems to positively impact bulb life.
Just as bilious green fluorescents aren't mine.... :-)
The message from "Dave Plowman (News)" contains these words:
True of most incandescant bulbs, but quartz-iodide lamps don't like running too cool. They rely on the envelope being exceedingly hot to stop the tungsten condensing on the inside, forcing it to redeposit on the filament instead. Mind you - they've got to be really yellow-orangey before it matters.
Indeed, this one has. But I bought TWO of the other dimmers, and one is still working fine (no soft start either). Can't remember the last time I changed the bulb on that one.
This seems to be a bit of an urban legend. I haven't had that problem at all over quite wide range of operating brightnesses, sometimes for several hours at low level.
According to the experts it is a myth, there is no redeposition cycle, and no loss of life through underrunning. The gas fill acts as a physical barrier to filament evaporation.
NT
hehe - so fussy :)
NT
Always ;-)
Which is bullshit for halogen lamps.
According to the manufacturers, the extent to which the halogen cycle stops when dimming depends on the power and geometry of the bulb. The halogen cycle requires a bulb wall temperature of at least 250C to operate. There is an upper temperature imposed by the pinch seals needing to be below 350C, or the conductors will fail by oxidation, although bulb area away from the pinch seal can be much hotter than 350C (limited by the softening of the glass/quartz material used, and the pressure of the halogen gas).
When you dim a halogen lamp, three significant things happen:
So the main factor for halogen blackening is if there is still any significant filament evaporation taking place when the bulb wall temperature drops below 250C. This is why it depends heavily on the power and geometry of the bulb. It will also depend on the level at which it is dimmed -- for a potentially susceptable lamp, operating it with a bulb wall temperature just below 250C verses just above 250C will make all the difference. Factors such as shielding from cold drafts can be very significant too.
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