Retrofit emergency lighting system

Claim 1

A ballast apparatus for operating at least one gaseous discharge lamp during normal and emergency modes comprising: a ballasting isolation transformer having a main primary winding and a secondary winding, one side of said main primary winding being connected to ground; a pair of input terminals connected across said main primary winding for connection to a source of AC power; a pair of filament windings wound in pancake form and arranged for connection to the at least one gaseous discharge lamp; said secondary winding connected to said filament windings; a second primary winding connected across said main primary winding, said second primary winding being magnetically coupled to said filament windings, said filament windings and said second primary winding being mounted laterally with respect to each other for providing a substantially low capacitance between said filament winding and said second primary winding; a first electrical insulation means connected between said second primary winding and at least one of said filament windings; an inverter circuit connected to said secondary winding for providing operating power during the emergency mode; said inverter frequency being in the range of 2.5 KHz and 4.0 KHz for minimizing capacitive leakage current and inductive shunt current; said inverter circuit connected to a DC power source; a case housing at least said inverter circuit, said main primary and secondary windings, said second primary winding, and said pair of filament windings; a second electrical insulation means lining at least a part of said case; a plurality of leads extending from said ballast case, said leads being of minimum length to make their connections so as to provide a substantially low stray capacitance.