Do incandescent light bulbs really burn brightest just before they burn out? Why?

James_M

Newbie

Posts: 1

Do incandescent light bulbs really burn brightest just before they burn out? Why?

« on: May 23, 2011, 01:16:13 PM »

Footnote [1]: To me, they always seem to burn brightest just before they burn out. ---Jim


	Logged

Don_M

Newbie

Posts: 1

Re: Do incandescent light bulbs really burn brightest just before they burn out? Why?

« Reply #1 on: May 23, 2011, 01:31:23 PM »

Electrical properties like resistance are actually nonlinear over the long term, NOT constant. Gradually, resistors like the filament in an incandescent bulb (which glows because the electricity is exciting electrons in the metal but can't easily flow through it) become MORE resistant. Because the resistance goes up slowly over time, the glow put off by the inability of the electrons to move through the filament without bumping into something and heating it up goes up also.

Not very scientific sounding but it's the basic principle.


	Logged

MidAtlantian2

Newbie

Posts: 17

Re: Do incandescent light bulbs really burn brightest just before they burn out? Why?

« Reply #2 on: May 23, 2011, 01:39:25 PM »

As an incandescent bulb 'burns', tungsten slowly evaporates from the surface of the filament - that is why bulbs gradually darken: this tungsten condenses on the inside of the glass - so the filament gradually gets thinner and thinner.

This thinning is not uniform, and where there are 'bottle-necks' along the filament, since the current is the same along the filament, that section will be brighter than the others.

And so you could say that, at least in parts of the filament, an old filament may burn brighter than a new one.

However, the darkening of the glass will always yield a net reduction in available light.

So, no, old incandescent light-bulbs do not give more light than new ones, they give less. Always.


	Logged

Pages: [1]

« previous next »