Martin Eastburn fired this volley in
news
I have a degree in Physics and 20+years as a EE. A heating filament is
simply to fast to see and the eye integrates the changes.


C'mon, you know very well that if you apply relatively high-impedance
supply across a filament, it will VISIBLY 'warm up'.

And that is simply because it's working in the very domain we've been
discussing, as a PTC resistor with a large coefficient of delta-R/delta-
T.

If you've never seen that, I'd say you need to go rig it up on the bench.
Nearly anyone who's ever done a stint as a tech would be familiar with
the effect.

Lloyd