Graphite light bulb

Thin refill begins to glow and give off smoke (graphite combustion reaction C+O2= CO2) when the electricity flow through the graphite-based mechanical pencil refill. The flowing electricity heats the graphite refill to an temperature about 1000K and emit visible light.

Graphite is one of the allotropes of carbon. Unlike diamond, graphite is a conductor, and can be used, for instance, as the material in the electrodes of an electrical arc lamp. The pi orbital electrons delocalized across the hexagonal atomic sheets of carbon contribute the graphite's conductivity.