What is an Arc Tube?
An HID light bulb contains two electrodes and noble gas. With the help of the noble gas, electricity passes through the bulb and between the electrodes in the form of an arc. That arc tube produces light.
What Causes an Arc Tube?
When an HID light bulb is turned on, a high voltage pulses through the bulb to ignite the arc. Simply put, the arc is a discharge resulting from ionized gas. Once the arc is established, the discharge can be maintained with a lower voltage.