Funny light-bulb and question about life time/rating

[edy]

I have one of these incandescent light bulbs (see below) used for a night-light. It turns out that the filament is a little loose in the bulb and if you jiggle the bulb sometimes the filament "crosses over" at a point in the middle, thus creating a short-circuit and making the net length of the actual filament that is being "used" for conduction much shorter than the normal length. As a result, the bulb gets considerably brighter.

I usually shake the bulb a bit and the filament is able to separate again where it is crossing over itself and the bulb goes back to being it's usual dim self, with the entire length of filament being lit.

So a few questions that may seem obvious but may be educational to the beginner and meant to confuse the issue:

1. As the filament shortens, the net voltage drop per length increases thereby causing more friction in the wire, leading to heat and light?
2. As the filament shortens, the resistance reduces and therefore amperage increases given an equal voltage?
3. As the filament shortens, there is less metal to dissipate the energy and therefore the shorter piece has more concentrated heat/light?

Is the bulb going to burn out faster? Is it safe to keep the bulb in the brighter state? Will it heat up more? Could it cause damage to the night light housing or create a fire hazard?

[IanB]

Yes, shortening the filament is like turning up the voltage. The filament will glow brighter and will burn out sooner (maybe much sooner).

It is unlikely to be harmful to the surroundings though. The filament is already white hot. A bit more white hot isn't going to make much difference.

[Whales]

1. Yes
2. Yes
3. Yes

Can't comment of whether or not it will cause a fire.  This depends on what it's mounted on/near.  It will definitely generate more heat and last less time.

The colour temperature of the bulb will also change (blue shift) due to the higher temp, but I'm not sure if it will be enough to notice.

[amyk]

https://en.wikipedia.org/wiki/Incandescent_light_bulb#Light_output_and_lifetime

Life is inversely proportional to the sixteenth power of the voltage, so I would highly recommend not leaving it in the partially shorted state.

If you half the length of the filament, it will approximately mean twice the voltage density, and that means it will last only 1/65536 as long. To put this into perspective, it means a lamp rated for 5 years will only last 40 minutes!