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So like most avid Mini fans I had a collection of about 30 Lucas sealed beam headlamps I had in a box doing nothing.
I decided to test them to see which ones were working and get rid of what I didn't need.
I individually connected the lamps to a 12v battery and each one lit up.
However some of the lamps worked for a split second and then filled with a yellowy gas and failed.
Somebody else I know had done exactly the same and we were both puzzled as to why this happened????
The sealed beams did not appear to be broken or cracked and it was a bit of a mystery especially as there did not seem to be rhyme or reason where some worked fine yet others blew??
'sure somebody on here will know. Cheers
PS I'm down to my last 16 so be quick with your answers

Oxygen has leaked into the unit. If there’s no crack, probably where the conductor passes through the glass and the element has then burnt.

Thanks. I initially assumed it was down to gas and a break in the seal but that was just an uneducated guess
Anybody want to buy 14 retro decorative decommissioned headlamps

You could paint Santas on them and hang them on the tree next month.

I might use the other 16 working units and really light the tree up

This is why you should never buy even a NOS sealed beam without having it tested first.

I bought a job lot of sealed beams a while back for £1 each because I knew that some would do just that, fill with smoke immediately. Sure enough of the 14 I bought 6 did that very thing.

Any sealed beam I sell has been tested on a 12v supply for 30 seconds. If there is a problem, they will smoke up immediately.

Agreed. Bloody annoying nowadays

There is however a trick which can be used to avoid immediately ‘blowing’ a lamp that has suffered from air ingress.

The reason for the milky residue is that the tungsten filament has immediately vaporized due to being heated to white hot in a partial oxygen [air] environment, instead of in a vacuum as designed.

If you have a suspect old lamp, instead of connecting to 12v connect it to three 1.5v batteries in series [4.5v total] or a 5v USB charger / power supply.

The filament will glow very dimly, but will not get hot enough to vaporize itself instantly. Leave it like this for 12 hours or until the batteries run out. Then, connect up the 12v but don’t leave it connected - just ‘pulse’ it a few times for fraction of a second each, allowing it to cool down each time.

As long as the air leaked in over a long time period due to a semi porous seal, i.e. there isn’t a hole, this process will gently burn off the oxygen content from the leaked air instead of vaporizing the filament immediately.

Once it has been completed, the lamp should be good as new to run on 12v.

Good tip that!

It makes perfect sense.

My option is to replace with the good quality Prefocused lamps that are currently being offered. These are a great option as they look "correct" but have options for decent modern "bulbs" too.

mk1 wrote: ↑Wed Nov 09, 2022 12:00 pm Good tip that!

It makes perfect sense.

My option is to replace with the good quality Prefocused lamps that are currently being offered. These are a great option as they look "correct" but have options for decent modern "bulbs" too.

Have you got a link?

Ta, I was thinking at the weekend I don’t remember Mini headlights being this bad!

This is a Lucas logo pre focus lamp with a halogen H4 conversion

It has been said elsewhere on the interwebs that you need to be cautious of fitting halogen bulbs to older original cars. The wiring needs to be in tip-top condition, and in some cases you are best off fitting a relay type circuit to power the bulbs as the original wiring and switches were designed for a lower wattage of bulb.