On Thu, 4 Oct 2007 10:24:38 +0100
"R D S" wrote:

I use 6v bulbs, 15 Watt.

I struggle to get hold of them locally, could I use a 12v bulb? And if so
what wattage would be best?

My understanding of bulbs is that electricity passes through the filament,
it gets hot and glows, so there would surely be interchangeability, is this
about right?

Not really. Although a 12volt bulb is unlikely to be damaged by having
6 volts across it, 6 volts will not get the filament hot enough to
give much light. I'm assuming this is an incandescent bulb.

To get advice on sources for your bulb, you'd need to say what kind of
fitting it is, or, better, post a picture.

R.