What quantity affects the brightness in a bulb?

When I include links in a post, the post doesn't seem to appear when it is submitted. If you google 'aqa as physics b past papers', the first option will take you to a site. Ty

Oh wow, that's brilliant!

For lamp B, the potential difference across it does not change, as the power source does not. Its resistance is obviously constant, and therefore it has the same wattage as it did previously.

The potential difference across lamp A does not change either, as any electrons travelling down that side of the parallel circuit still have a set amount of voltage to 'loose'. As the resistance has decreased the current must increase, resulting in a greater wattage for lamp B.

I guess my mistake was assuming there was a fixed amount of 'brightness' to share between the lamps.

Thankyou very very much, you really opened my eyes to that one, thankyou!

The thinner the wire, the higher the resistance.
The thin wire glows mainly due to its high resistance turning electric energy into heat energy, which in turn heats up the wire and makes it glow red due to incandescence. (Like a light bulb.)

Refer -->https://en.wikipedia.org/wiki/Incandescence