Sparks

The sparks are produced when the voltage on the domes gets large enough that it ionizes the air, turning it from an insulator into a conductor. This does not all happen at once, but it does happen very quickly--a typical spark (or lightning flash) lasts less than 1/1000 of a second!

Only one spark can be produced at a time, although sparks can come very quickly. Each spark drains the electricity off the domes and the machine must then re-charge itself. In this our machine differs somewhat from a lightning storm where the cloud has such a massive charge that most lightning strikes are actually two to ten or more strokes using the same channel.

In this picture you can see a fainter "echo" of the spark near the top of the picture. This "echo" is actually caused by reflections inside the lens of the camera. It is much closer to the true size of the spark--the spark itself is so bright that it overloads the camera, causing it to appear much wider than it really is.