Packaged add-on device for lead-type ballast and luminaire which incorporates such packaged add-on device

Add-on device for lead-type ballast comprises additional inductor and series-connected controlled AC switching means which are connected in parallel circuit with the capacitor portion of the lead-type ballast such as is used to operate an HID sodium lamp. The add-on device has a sensing and control circuit which operates to sense a lamp operating parameter in order to control the actuation of the AC switching means which in turn controls in predetermined fashion the operation of the ballasted lamp. The inductor and AC switch and sensing and control means of the add-on device are all packaged within a can-shaped member which has dimensions similar to those of the conventional capacitor can for the lead-type ballast. All the elements of the add-on device are potted within the capacitor can with terminal means extending from an end portion thereof for ready connection along with an exposed potentiometer portion to enable the control to be adjusted. The usual luminaire which utilizes a lead-type ballast normally incorporates one capacitor, although most luminaires are provided with the space for an additional capacitor, even though it is not needed. The present packaged add-on device readily fits into their available but unused space so that it is readily incorporated into existing luminaire designs.