Abstract: A safety circuit is provided for a ballast of an electro-luminescent (EL) lamp. The EL lamp had an electrical ground shield on at least a portion thereof and has a separate ground lead. The ballast is an isolated ballast with a line input being isolated from an output. The ballast is constructed and arranged to be electrically connected with the separate ground lead. The circuit includes a current sensing structure constructed and arranged to connect between the separate ground lead and a potential ground of the ballast. In the event a user contacts the EL lamp to replace the EL lamp or contacts a defective EL lamp, the ballast is shut down based on a value of current sensed by the current sensing structure.

Abstract: A ballast (11) includes a variable output DC converter source (12) and an inverter circuit (14) arranged to provide AC output voltage to an electro-luminescent (EL) lamp (16). A Q factor of EL lamp can characterize the age of the EL lamp. A series resonance-parallel loaded circuit and two voltage detector (18, 20) are constructed to measure the Q factor. A processor (17) controls the output of DC voltage source in accordance with a look-up table containing constant brightness algorithm based on the derived voltage and Q relationship.