<P> These hazards are not present when the arc is formed outdoors since the heated ionized gases will rise up into the air and dissipate into the atmosphere . Spark gaps which only intermittently produce short spark bursts are also minimally hazardous because the volume of ions generated is very small . </P> <P> Arcs can also produce a broad spectrum of wavelengths spanning the visible light and the invisible ultraviolet and infrared spectrum . Very intense arcs generated by means such as arc welding can produce significant amounts of ultraviolet which is damaging to the retina of the observer . These arcs should only be observed through special dark filters which reduce the arc intensity and shield the observer's eyes from the ultraviolet rays . </P>

Why does a tesla coil need a spark gap