Bulb ratings and fittings

[Andy Burns]

But a bright light will stop down your iris, so it acts somewhat like a pinhole, assisting the eye's lens ...

[Tim+]

Well thanks for snipping the rest of my reply that made it quite clear that it isn't nearly as simple as that.

Tim

[tabbypurr]

Some power resistors are only specified for claimed power dissipation at minus 100C!

NT

[The Other Mike]

What temperature rating capacitor would you expect to be fitted and why would it 'boil' at 105 deg C?

[The Other Mike]

Care to point to a datasheet that shows that?

[T i m]

I'll have a go and say '105 DegC' cap and it would 'boil' (read not be happy at ..) if 105 DegC was the temperature of the fitting and therefore the temperature it was working at? Maybe the caps are more susceptible to overtemp than most the other components?

I'm not confirming (scientifically) that that's what will happen but that it seems logical as a suggestion to why such things might fail prematurely if they are allowed to run hotter than they 'should'?

Cheers, T i m

[Tim+]

What, in a 60W rated lamp?? Recklessly dangerous.

Tim

[The Natural Philosopher]

No, it isn't. Its somwhere between 175 and 200C

But LEDS are of course not silicon devices....

[The Natural Philosopher]

75C is standard commercial rating 125C is milspec. Silicon Semiconductors are rated differently with 150-200C junction being the critical temperature.

GaAs LEDS generally operate at sub boiling point junction temps, say 60-80C

[The Natural Philosopher]

Apperently its all OK if fitted by a fully paid up member of the sound engineers and transverse wankers union, then its just fine...

[Martin Brown]

That is about when the water based electrolyte in a cheap electrolytic capacitor starts to turn into steam. Capacitors bulge after that until the pressure relief bursting disc pops. You can get capacitors with higher temperature ratings but I have never seen any in a lamp PSU.

Capacitor failure by drying out or boiling is invariably the weakest link in the typical lamp driver PSU. There are capacitors rated for 125C that have an MTBF of 2000 hrs which is no better than a filament bulb.

Quite difficult to test long term batch reliability too which is what led to the dodgy capacitors with the misformulated stolen electrolyte wrecking quite a lot of motherboards a decade or so back.

[whisky-dave]

There's no evidence they'll boil but the electrolyte will dry out the highe r the temperature, the 105 is the maxium working temeprature and at that th ey are gurenteed to last say 1000 or 2000 hours as a minium, you can get 13

0C caps if really are running at high temps.

[tabbypurr]

NT

[Dave Plowman (News)]

No, Tim, unlike you I understand such things. If a fitting is rated at 60w tungsten and not bright enough, I'd not have bought it in the first place.

However, for those that have, it might be possible to uprate the size of the tungsten lamp it can take by fitting a more heat resistant holder. Brass and ceramic rather than plastic.

It also depends on how long it is on for. The rating will be for continuous use. If only for short periods, can likely be exceeded safely.

Basically, it is an idiot's guide. Ring any bells?

[whisky-dave]

Not sure where it proves what you say it says.

[Tim+]

Understand what though? Clearly not understanding that selective quoting can turn almost anything anyone says into nonsense.

If you don't like it, don't do it.

Tim

[harry]

It's about lamp life. Incandescent (filament)lamps can stand a lot more heat than CFLs. (To do with the inbuilt electronics). So the fitting has separate ratings for each of them. Obviously it will be a lot hotter with incandescent.

[Dave Plowman (News)]

I snipped it because it was incorrect. And replaced it with an accurate one.

BTW, you might get yourself a proper newsreader which 'snips' sigs. All good ones do.

[tabbypurr]

her the temperature, the 105 is the maxium working temeprature and at that they are gurenteed to last say 1000 or 2000 hours as a minium, you can get

130C caps if really are running at high temps.

Dave is scientifically thorough, he doesn't just take your word for things, he requires evidence that water boils.

NT

[Tim+]

The first paragraph was just an illustration of many folks incorrect thought processes, not an assertion. My second paragraph was correct.

Snipping it to add your own "correction" was just dickishness.

As to newsreader digs, get a life.

Tim