bulb failure - why?

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wonder if anyone has come across this before. both the bulbs in my bow lights have gone phut. one is open circuit on a meter, the other has the expected resistance. under magnifying glass, both filiaments are OK. both sets of terminals are OK too. but neither will light at all.

I have replacement bulbs ( would you believe £14 for two bulbs?) but am curious about how these two have failed. incidentally the two are different makes, ages and designs.

any ideas?
 

Stemar

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wonder if anyone has come across this before. both the bulbs in my bow lights have gone phut. one is open circuit on a meter, the other has the expected resistance. under magnifying glass, both filiaments are OK. both sets of terminals are OK too. but neither will light at all.

I have replacement bulbs ( would you believe £14 for two bulbs?) but am curious about how these two have failed. incidentally the two are different makes, ages and designs.

any ideas?
[pure speculation]
Vibration is a great bulb killer, and could account for the one with the open circuit. As for the other, assuming a new bulb works in its place, I'd suspect corrosion on the contacts. Another possibility is that vibration got it as well, and the broken bit, wherever it is makes contact when you tested it in one position, but doesn't in the light.
[/pure speculation]
 

noelex

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A coincidence is the most likely explanation, but there may have been some contributing factors.
As the first bulb failed the voltage drop in the wiring would be reduced. Bulb life is very dependent on voltage. The voltage would still be within specification, but an increase of 0.2v or can be the final straw for an old bulb (particularly if you were motoring wth a high battery voltage when they failed).
Bulb also don’t like a rapid change in temperature so rough passage where the holders are hit by waves can be their demise (although they should both go open circuit in this case)

It is possible you had a voltage surge, but bulbs are tolerant of these and I would expect other electronics to have been damaged first and once again both should be open circuit.
 
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OK but if they had gone open circuit, there would have been a break in the filiament. And under a magifying glass, I cannot see a break in either. And one of the bulkbs is definitely not open circuit in that it gives the sort of reading you would expect on an ohmeter.

Not bad contacts - both are clean and shiny after a bit of polishing.

Have tried both with the 12v regulated supply from my ham radio and still no life.

Weird.
 

elton

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Filaments sometimes look intact, but if you look closely then flick the bulb, you can see the break.

A multimeter will sometimes give a false reading of continuity, in that it will show continuity with the low current the meter is sending through it, but it will not pass a large current. I'd expect it to work if the contacts were cleaned properly.

There's always a simple explanation for problems like this.
 

KellysEye

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All the bow bulb failures we have had have been caused by corrosion at the terminals or broken wires. Both of those are caused by waves hitting the lights 9water ingress) and cabling (flexing it). What I don't understand is why bow lights aren't waterproof.
 

jordanbasset

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All the bow bulb failures we have had have been caused by corrosion at the terminals or broken wires. Both of those are caused by waves hitting the lights 9water ingress) and cabling (flexing it). What I don't understand is why bow lights aren't waterproof.

Yes we had the same issue, the wire itself also needed cutting back about a foot to get a clean connection
 
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