Let me explain. My son has a small typical night light that occasionally will go out, even if the bulb isn't dead. Usually I'll tap on it repetitively or shake it to get it to work again. When I hold it under another light, I can see the "coils" or string-looking things moving around uncontrollably, unattached to the points. Now, here's the weird thing. Sometimes, when I get it to work again, it will actually appear brighter than before. Usually it's an orangey-yellow dim light, but after it goes out and I "fix" it, it becomes whiter and brighter. How can this be? Is it because the coils are no longer connected in their usual triangular shape, instead forming an irregular shape? How could that effect it?

It looks something like this. Just your average night light

  • \$\begingroup\$ It sounds like there is a loose electrical connection in the lamp somewhere. Considering that you "fix" it by tapping it, I would seriously consider either replacing the entire lamp or getting a qualified electrician to mend it. Maybe there is somewhere like a domestic applicance repair place near you - they would be able to check and repair it for you. \$\endgroup\$ – Andrew Morton Jan 6 '17 at 21:25
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    \$\begingroup\$ If the filament is not attached to its holders, it could be simply shorting out a small section if the coil touches in two places (hence it would get brighter). Solution? Don't lose sleep over it, just get a new bulb... \$\endgroup\$ – Tom Carpenter Jan 6 '17 at 21:25
  • \$\begingroup\$ @TomCarpenter That's what I thought at first, but I've never known tungsten filament lamps to be repeatedly fixable with percussive maintenance. \$\endgroup\$ – Andrew Morton Jan 6 '17 at 21:27
  • \$\begingroup\$ I was meaning a photo of the actual broken/misbehaving one, but worry not you have your answer. \$\endgroup\$ – Tom Carpenter Jan 6 '17 at 21:39
  • \$\begingroup\$ This is common on some types of lamp with very flexible poorly supported filaments. If it goes out and sometimes lights with a tap then the buld is burnt out and needs replacing. The risk of fire is fractionally increased as it may dissipate mote heat and run hotter but usually the filament will burn out again if it is far outside the design current. Replace with LED lamp if you want it to be mechanically more robust in future. \$\endgroup\$ – KalleMP Jan 7 '17 at 15:16

The coil is a resistor lets say its divided into three parts, they all have equal resistance (same material). If the coil in the bulb comes loose, it can short out at a different point. You have less resistance and more current through the same section of coil. This will make it brighter and also hotter and reduce the lifetime of the coil.


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Does this also mean that the current consumption can quite double in rare case? If it is controlled by a relay or a switch, then the whole design is subjected to stress. This is a good example for use case stress test. \$\endgroup\$ – Umar Jan 7 '17 at 4:46

I've seen that before. You have a burned out incandescent bulb. The tungsten coil filament has disconnected from one end, but is being held onto the other reasonably well, and is acting like a spring. If it's jostled, the coil will sometimes strike its terminal and reconnect for a time.

When it does, there's no telling what part of the filament will connect, and as laptop2D describes, that's either cutting out part of the element (making it brighter) or paralleling elements that were meant to be in series (likewise).

I doubt it can overload like this for very long. Perhaps it's not overloading, and the effect you see is just a trick of perception.


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