Blowing GU10's

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.