Cheap lightbulbs?

[steve447]

Mate at work today has brought in a bulb that was in a wall light, when his kid turned on the light last night there was a huge bang.
MCB didnt trip, but the glass bulb has completely detached itself from the metal and the bulb was upside down in the fitting so it must have jumped a fair bit.
Its a 60W bayonet, candle shaped bulb and has poundland written on it. There is a fair bit of scorching on the glass.
i have heard of bulbs exploding due to temp change but have never seen a bulb detach it self from the metal before.

Do you reckon its just cheap and not so cheerful bulb that is the culprit?

I have tried to attach a image of the bulb but it wont let me upload it from the work computer.

 

[Rockingit]

I had another friend on facebook yesterday saying she'd had a glass bulb explode all over her for no apparent reason.

My personal theory is that it's cheap, cheaper and shockingly [mods - "not very good"] imports from Chinese knock-off shops entering the UK retail chain.

 

[Marvo]

I've never seen one actually go pop in the fitting but I've seen a lot of cheap lamps where the glass completely detaches from the base. If the fitting is shadeless or coverless then I'm sure the glass would fall to the floor and implode giving the impression it exploded.

 

[Flying Ninja]

I Have had this a few times buying lamps from Asda. Put a BC 80w in pendant and bang as soos as it turned on and glass everywhere. ( I only purchased from asda as always forget when in wholesalers about my own home).

If it is an es fitting, then sometimes if not screwed in properly this can affect lamp life.

It could be a conspiracy to make everyone switch over to energy saving by reducing the quality.......

 

[wade88]

Im having this same trouble at the moment with a customer.

Just finished the re-wire of her property and supplied all the bulbs (which i am instantly regretting). the bulbs came with the contractor pack of downlights so i wasnt expecting amazing quality at all, however upon initial turn on, 2-3 went down which was fine, replaced those straight away. But now a week or so later shes coming back to me saying 40% of the 50w halogen spots have all gone out?! is it just cheap bulbs that are responsible?

 

[Rockingit]

I've just started to re-fit my own house a bit at a time with Halers LED's for this very reason - stuff efficiency savings, I'm bored with replacing GU10's everytime a door slams upstairs!! Did four last night, 27 to go.....

 

[wade88]

Rocking it mate what is it then that promotes such a high count of bulb blows, or is it literally things as spurious as doors slamming and shaking the fitting? I know its an insane question to even be asking on this forum "why are the bulbs blowing" but its just causing me so much hassle, they are starting to see it as me being a cowboy and having done a poor job, but everything has tested out fine, there are no problem snaywhere, but they just keep blowing? Im getting a bit fed up of getting snide messages and patronising comments from them over something so trivial and completely out of ym control, considering dropping off a bag of candles and telling them to just pipe down

 

[Marvo]

Lamp life or 'bulb' life is something I looked into before and came to the conclusion there several reasons they fail prematurely such as poor connections, voltage fluctuations, humidity, rapid switching on and off etc.

One thing that's worth pointing out is the way they establish the lifespan when the stamp the box with 20000 hours for example.Mostly, lamp life is stated according to IEC60969 standards.

Quote from IEC60969;

• Tests are conducted in a draught proof cabinet at (25°C) and a humidity of less than 65% with a stabilized and optimized supply voltage.
• The measured life to 50% failures (average life) shall not be less than the rated life to 50% failures (rated average life)

In short the lamp life stated on the box refers to the length of time of operation at which point at least 50% of the lamps from a random sample batch of at least 20 lamps should still be working (assuming controlled humidity and temperature, assuming draught-free conditions, assuming perfect electrical supply and running conditions ie. no frequent on-off switching.)

In short ....they cheat and you'll be lucky to get half the life stated on the box when the lamp is used in real-life conditions.

 

[Rockingit]

Agreeing with the above, I think there's also a little bit of probability maths comes in, too:

On the basis that you rarely if ever replace 1 x pendant for 1 x downlight, typically it's four, or six or whatever based on the ceiling size, then if we take a sample period of 100 hours, rather than having the chance of a bulb blowing being 1:100, it's now 1:25 or 1:16 or whatever. So yes, you WILL get 'more blown bulbs' just because there are more bulbs to blow, pro rata.

Therefore, there is an apparent problem BEFORE we start on anything more physical.

As far as the physical then goes, GU10's are fragile when hot - the same as most filament lamps. So if you've got a line mounted in a hallway ceiling, say, sitting on 11mm of plasterboard nailed to 150mm of joist, then 15mm of chipboard floor, then a herd of thundering elephants at play above it (sorry - I meant 'children') then that vibration has to go somewhere. The thing that's got the most movement available to it is the filament, happily swaying there in it's little glass house. Add in some more electrical factors like connections, voltage fluctuations etc, and you start to see a rapid decline in reliability.

You don't tend to see the same influences in commercial and shop applications as the environmental factors are different.