The GDV was developed by Prof. Konstantin Korotkov at St Petersburg Technical University in 1996. Essentially, the photon and electron emission from an object's surface is stimulated by electrical impulses. This results in an electronic avalanche effect creating a series of impulses or "sliding gas discharge".  The Gas Discharge Visualisation (GDV) is named after this well-known physical phenomenon.

The fact that a human emits light when subject to electro-magnetic field is not new. Nicola Tesla discovered such effect in 1880 and the work of Semyon Kirlian in Russia during 1940s is well documented.What is unique about the GDV technique is that the visual discharge can be photographed using powerful digital cameras and then analysed by sophisticated computer software.

Different objects display a different glow. Prof Korotkov and his team have since shown that GDV parameters such as intensity, area, and form, are reliable and sufficiently distinctive between various objects. In people, the type of the GDV image reflects the activity of the autonomic nervous system and gives an insight into the physiological and psychological states of a person. 

Link to Prof Korotkov's website