Editing Neon lamp (section)

=== Voltage tester ===
[[Image:Neonlamp3.JPG|right|thumb|+DC (left), -DC (center), AC (right) supplied to NE-2 type neon lamps|alt=Photograph of 3 small glass capsules. Each capsule has 2 parallel wires that pass through the glass. Inside the left capsule, the right electrode is glowing orange. In the middle capsule, the left electrode is glowing. In the right capsule, both electrodes are glowing.]]

Most small neon (indicator-sized) lamps, such as the common '''NE-2''', have a [[Breakdown voltage#Gases and vacuum|break-down voltage]] of around 90&nbsp;[[volt]]s. When driven from a DC source, only the negatively charged electrode ([[cathode]]) will glow. When driven from an AC source, both electrodes will glow (each during alternate half cycles). These attributes make neon lamps (with series resistors) a convenient low-cost [[Test light|voltage tester]]. By examining which electrode is glowing they can reveal whether a given voltage source is AC or DC, and if DC, the polarity of the points being tested.