Lots of ons and offs in that situation?
Brian
Lots of ons and offs in that situation?
Brian
There you have it. I long ago discovered B&Q bulbs don't last. I now only buy from TLC.
"Dave Plowman (News)" wrote in news: snipped-for-privacy@davenoise.co.uk:
I have GU10s in two rooms and I cannot recall how long they have lasted - certainly more that 3 years. They are both fed from a touch dimmer which gives a soft start.
I've also got a fair number of these too. Decent makes seem to last about the same as any tungsten bulb - just not B&Q own brand.
No not really. On when it gets dark, off when he goes to bed.
I figure (using P = V^2 / R ) that going from 230 to 242 V increases the power by 10%. Why does that cut the life by 50%?
(I'm not arguing, but curious about the physics behind this.)
probably for the same reason a 1A fuse will take 1A indefinitely but blows at 1.1A. :-)
Not all physics is smooth linear differential equations.
I mean what difference does it make if my rifle bullet is 6" out at half a mile? I will obvious kill the person 99.99% instead of 100% wont I?
This is what is hard for people to understand, TNP, even though they experience just that every day in their own lives.
That's a lot more substantial than a 50% decrease in life.
Ha, you got me there. But seriously, I was hoping for some explanation involving the dissipation of the extra 10% of heat generated.
I _think_ the bulb life is limited by the filament evaporating. Take the temp up a little, and it evaporates much faster - it's an exponential relationship.
Andy
It's a very fine relationship between efficiency and life. Drop the efficiency and the life goes up dramatically. Think of, say, panel illumination lights on a car versus headlamps - the headlamps are likely to fail three or more times as often.
when clearly that cant be the failure mode? I'd look at oxidation at or around the operating temperature. I bet that's a sharp knee.
Or whether in fact the material strength starts to undergo a transition at that temperature
To get light efficiency you run filaments as hot as they can go.
The formula quoted in the wiki (don't know its source) is:
new life / old life = ( old voltage / new voltage ) ^1^3
(that raised to the thriteenth power in case it does not look ring in ASCII)
so 1000 hours at 230 volt would become:
nl / 1000 = (230/240)^1^3 = 0.58
so life = 1000 x 0.58 or 580 hours at 240V.
They aren't lasting that long. It's a matter of weeks.
Changing the subject slightly.
I wonder if people understanding of bathtub curves has altered, now that baths come in so many strange shapes?
The cross section is basically the same regardless... ;-)
That's rather like what I meant by heat input & dissipation. I guess in your example, a 10% increase in heat generation is enough to push the temperature over the edge.
Lengthways or sideways :)
I always use the length. Give you the chance to have a different slope at the two ends.
Andy
Far out: you don't run into 13th powers very often.
Fnarr fnarr.
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