Systems and techniques for identifying that a load associated with a lamp is absent from a circuit is described. A method, for example, includes receiving output of a circuit having at least two loads associated with a lamp and an anti-parallel transformer, monitoring, based on the output, a resistance of the anti-parallel transformer with respect to a threshold corresponding to the associated loads, and identifying that either the first of the associated loads or the second of the associated loads is absent from the circuit responsive to the monitored resistance crossing the threshold.