Incandescence

If temperature rise... the resistance of the wire increases.

Thus reducing the current....which reduces the heating

So the temperature comes down....so the resistance decreases.

So the current goes up...and the temperature rises again...

So it regulates itself to a stable temperature/current.

Not so I'm afraid Del

The traditional filament in light bulbs was nichrome wire which has a negative temperature coefficient.

i.e, when it heats up there is very little resistance change, unlike copper wire whose resistance increases when heated, thereby requiring as to calculate volt drop!

At switch on, a filament lamp and the traditional electric fire both take excessive current, then it lowers and stabilises as the filament reaches operating temperature. This is why light bulbs usually blow when you switch them on and not when actually lit, because of the initial excess current flowing through the wire element.

Try PAT testing a 3kw electric fire - most of them will fail on excess current because PAT testers usually supply only up to 3KVA, but if you switch the fire on for a couple of seconds and then test it - it will be OK.

Many years ago on Tomorrows World a company showed a light switch invention that only allowed a filament lamp to switch on when the AC current was at the lowest part of the cycle and not the maximum, (the original soft start light switch), as a means of extending the life time of filament lamp.

It never caught on because it needed an extra pilot wire to be run from the switch to the light position and because filament lamps have now been largely superseded.

Th amount of heat or light from the filament is dependent upon the resistance and size of wire - obviously the lamp has a very fine wire so that when the current flows through that wire it glows incandescent white. The wire is very hard and will not burn through easily. The filament lamp produces almost as much heat energy as it does light so it is very inefficient, but it is well over a hundred years old now and we have not improved upon it much until recently with LED and Compact fluorescent technology.

For obvious reasons you would not want an electric fire to burn incandescent white so the element wire is thicker and doe not produce so much heat.

Th best burning position for a filament lamp is vertical with the glass bulb upwards so that all the heat is dispersed through the entire surface of the glass envelope, the second best position is vertical with the glass downwards but the rising heat gets trapped at the metal cap end and eventually cases overheating and failure.

The worst position is horizontal especially if one of the filament holders is in the vertical most upwards position as it take all the rising heat from the whole filament ands leads to early failure. It is no so bad of the filament is horizontal and all the heat can escaped up through the glass uniformly - it all depends on the position of the lamp holder in the chandelier - so when you wife asks you why these lamps keep blowing - you could tell her - but it will probably be your fault anyway for letting her buy that light fitting in the first pace.

!!!

You don't offer any explanation!

Can you answer the original question?

Hang on a minute!....you say

At switch on, a filament lamp and the traditional electric fire both take excessive current, then it lowers and stabilises as the filament reaches operating temperature

Which is exactly what I said!!!

And another thing! (lol)

So how come I can use a small filament bulb to amplitude stabilise the output of my Wein Bridge Audio Oscillator????