On 29/10/2010 11:57 p.m., Tim Streater wrote:

yes. Thermal coefficient of resistivity.

Current will in fact be a lot higher.

Plus the fact that even for a tungsten blub run normally, the energy peak is in
the infra-red, below the visible range. Under-running just shifts the peak
further down.


Let's see if I understand this correctly. Even if the bulb did dissipate 7.5w
at 120v (and presumably the power would be lower than that, because the filament
resistance would be higher than when the bulb is used with 230v), this would
give a filament temperature much lower than when the bulb is dissipating 30w,
causing more radiation to be emitted in the non-visible range (infra-red). So
it seems I was wrong twice.