first make sure that the discharge does not emit light is too bright, and its spectrum is not present in quantities of dangerous ultraviolet radiation.If there is at least one of these factors, using specially selected for such cases filters.Beware also of ozone, electric shock, and if you are going to observe the discharge between the electrodes containing carbon - carbon monoxide poisoning.Take appropriate measures to protect against these factors.
If before you short discharges, sometimes repetitive, the channel of ionized gas is in the form of a thin cord, at each discharge can be heard crackling - discharge is a spark.
If you see a continuous discharge between the electrodes is very hot (sometimes hot, and even white-hot), it takes place at a pressure close to atmospheric pressure, or even exceed
it, to conclude that it is an arc.Such a discharge is almost silent, but when AC power can honk.The voltage drop between the electrodes may be only a few volts, and currents can reach hundreds of amperes.
Look at conventional fluorescent tube.Electrodes warmed it hot, but they are not visible due to the intense glow of the phosphor.Thermionic emission is as arc discharge.Bowl pressure below atmospheric pressure.The current density therein is relatively large, but less than the arc discharge.It occupies an intermediate position between the arc and glow.
compare this interim "glow-arc" with the usual glow discharge.The electrodes in the present glow discharge although warmed up, but not so much that they glow was visible.Their heat is clearly insufficient for the emergence of thermionic emission.Bowl pressure below atmospheric, the current density is small, and the discharge channel is in some instances is translucent.
If you find yourself weak on steady only one electrode hiss, the phenomenon takes place at atmospheric pressure, to conclude that the level - the crown.This is the only rank that does not have a negative dynamic resistance, because not always require current limiting to prevent escalation into other categories.It creates electromagnetic noise over a wide range.