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Registered Member #1617
Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139
Hi all,
Recently I've had many light globes (regular 240v 100w incandecent globes) violently 'detonate' rather than die quietly (as used to always happen). It inevitably occurs when you switch it on, the glass envelope is ejected from the metal bayonet base at a high velocity, acompanied by an extremely loud bang/flash (seems like a dead short across the mains, as it always trips the breaker). The bulb seems to be fully intact when it leaves the fitting (i have had at least one not break when hitting the floor/wall/table etc), and the metal base is always completely charred and mangled (requires pliers to remove from socket) It has also ocasionally broken (!) the plastic light socket itself. Please someone tell me I'm not insane, and this happens to other as well. This has only been occuring recently, and is now quite frequent. It seems that the quality of incandecent globes is falling. Not to mention it wouldnt be to good to have a shard of hot glass hit your eye, luckily, its missed every time so far!
Its been getting to the point where I feel like taking cover every time i switch the light on. Whats going on?!
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Have you recently mesured your mains voltage, it can be due to higher than normal voltage, or alot of transients on your supplylines, you could invest in a transientprotection even thou I think they are meant for lightning surges rather than small peaks.
The light output and lifetime of lamp filaments is known pretty accurately as a function of voltage. Briefly: the amount of light that a bulb produces goes as the 3.5 power of the voltage ratio. The lifetime goes as the inverse twelfth power of the voltage ratio. This is for a normal light bulb. Also, the current goes as the 0.55 power of the voltage ratio. Voltage ratio is the applied voltage divided by the rated voltage.
So, for example, if a 220V bulb is operated at 110V, the voltage ratio is 0.5. The light output will be 0.5 raised to the 3.5 power, which is 0.088. It will be very dim! It will make less than one-tenth as much light as if it were run on 220V. It will also be orange in color.
The bulb will last a LONG time at this low output. The lifetime will be increased by 0.5 raised to the inverse twelfth power, or 2 raised to the twelfth power, which is 4096 times as long! It will last for thousands of years.
For example, suppose a 120V bulb is driven at 140V. The voltage ratio is 140/120 = 1.167. The light output is 1.7 times as much. The actual power consumed is 1.27 times as much, so the bulb is more efficient. However, the lifetime of the bulb is cut down by a factor of 6.35.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
I have had that happen at least twice and yes the average quality has dropped a lot. I have also had problems with the energy saving ones too that keeps exploding the capacitors in a very violent manner.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I think there should be a fuse in the base of the bulb, and I won't be surprised with today's production moving to china if they put in some kind of an explosive fuse...
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Perhaps it is a combination of mains surges, switch on thermal stress, and poor manufacture - are they all from the same manufacturer? I'm sure the same thing has happened to me in Blighty from time to time.
As for the compulsory 'low energy' types we all have in Europe now, I've never known one last X,000 hours or whatever it is supposed to be. Some are good and last a long time, but others are really bad value.
No one would make any money out of an everlasting light bulb!
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Harry wrote ...
As for the compulsory 'low energy' types we all have in Europe now, I've never known one last X,000 hours or whatever it is supposed to be. Some are good and last a long time, but others are really bad value.
About five years ago we bought some Philips CFLs and all of them are still going, some are used a few hours every day. I think they have several X,000's of hours on them so I think it's a matter of "luck"
However the quality of most products has gone down dramatically in the last few years, it's often difficult or even impossible to find a quality product, even if cost is not an issue...
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
It is quite common for bulbs to go short-circuit (at least temporarily due to arcing when the filament fails) However the energy in this event should be limited. I would check your fuse / circuit breaker rating for the lighting circuit in your house if things are exploding violently.
Have you had any electrical work done prior to bulbs starting to explode!?!?!?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I had this happen to me only once in my life, when I was a kid. I was lying in bed reading, and the bulb in the reading lamp exploded just like this. There was a huge flash and bang, and the glass bulb shot out of its metal base and hit me in the ear. It gave me a hell of a fright.
This was in an old house with wired fuses, so there was lots of fault current available. As far as I know, the explosion is caused by a poor quality fuse inside the lamp. All light bulbs have a "Ballotini fuse" but in some of them it fails to blow properly, in which case either the breaker trips or the bulb explodes.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
eeeek! this sounds plausible. could also be water getting into the cement.
could also be use of cheap "sand" that is partially conductive, eventually conducting whiskers might grow from the solder blobs inside and trigger a short..
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Unusual lightglobe faliure mode
rather than die quietly (as used to always happen). It inevitably occurs when you switch it on, the glass envelope is ejected from the metal bayonet base at a high velocity, acompanied by an extremely loud bang/flash (seems like a dead short across the mains, as it always trips the breaker). The bulb seems to be fully intact when it leaves the fitting (i have had at least one not break when hitting the floor/wall/table etc), and the metal base is always completely charred and mangled (requires pliers to remove from socket) It has also ocasionally broken (!) the plastic light socket itself. Please someone tell me I'm not insane, and this happens to other as well. This has only been occuring recently, and is now quite frequent. It seems that the quality of incandecent globes is falling. Not to mention it wouldnt be to good to have a shard of hot glass hit your eye, luckily, its missed every time so far! 
so I think it's a matter of "luck"
