A luminous electric display unit is disclosed in which glass tubing containing inert gas such as neon is entirely or substantially enclosed within a protective housing, thereby providing protection both for the glass tubing and the public. The rapid oxygen consumption at a time during the growth of bacteria resulted in a sharp decline of the cathodic peak current curves. The safety shield is urged in a direction away from the needle hub by a spring located between the needle hub and the safety shield. Moreover, each capsule includes a feedthrough, which electrically connects one or more components therein to circuitry on the circuit board via a plurality of leads.