The term 'discharge lamps' covers many of the lights we use today and the most common is the fluorescent light. Like all discharge lamps, light is created through the stimulation of atoms/molecules in a specific gas/metal vapour mix. Fluorescent lamps contain a mercury vapour suspended in either neon or argon gas. The mercury vapour is excited by electrons that are emitted from a cathode which converts this into a photon of light (usually in the UV and in narrow wavelength bands). This light then interacts with a coating on the inside of the glass envelope. This combination of fluorescent and phosphorescent material absorbs the UV light and then emits the broad spectrum we perceive as 'white light'.
Gas vapour discharge lamps are based on the same technology as fluorescent lamps but use higher pressures and higher power, allowing a far greater light output to be generated in a more efficient manner. They also use different gas/metal vapour mixtures that exhibit an extended spectral output that does not require any phosphorescent/fluorescent coatings inside the glass envelope. The most familiar type of high intensity discharge lamps is the xenon lamp, using xenon for light generation.
For vision applications, this type of light source is often used when a large amount of light is required over short periods of time, such as for strobing applications to freeze the motion on a fast moving production line. Other uses include situations where a very high light output is required over a large area as is sometimes the case in robotic applications.