Carbon filament

This is a bulb with a low wattage, spiral carbon filament. It is similar to some of the early electric filament bulbs by Swan and Edison. It is used in the Science department at school to teach light and optics: the low power and distinctive shape of the element make it ideal for studying how lenses focus images.

I also think it makes a rather attractive, slightly abstract design, with the distorted reflections of the filament in the glass envelope of the bulb.

EU rules on incandescent lights make these rather difficult (and expensive) to get hold of now.