Abstract
The filling gas pressure of mercury-free HID lamp is much higher than that of the mercury containing lamp. A high filling gas pressure leads to a high ignition voltage in mercury-free HID lamp and this makes the ballast with ignition circuit bigger and heavier in order to maintain the ignition reliability. Therefore, it is important to decrease the ignition voltage of mercury-free HID lamps. It is necessary to better understand how the discharge starts and grows in the HID lamp burner in order to decrease the ignition voltage. An ultra high speed camera was used for the discharge observation, the shutter speed of which is 5 ns. As a result, we found that a very weak discharge occurred outside the burner before the burner ignited. It is believed that this weak discharge influences the ignition condition from two points of view, which are the ultraviolet rays radiating from this discharge and the electric field distortion formed by the attached electric charge on the outside of the burner wall. We found that the attached electric charge on the outside of the burner wall strongly influences the ignition performance and that the ultraviolet radiation little influences the ignition performance.
