The deflagration-to-detonation transition (DDT) of low density (0.88 g/cc) PETN during exploding bridgewire (EBW) initiation has been studied using laser interferometry and streak photography. Cutback experiments using VISAR have confirmed a 1.0 mm run-distance to detonation in this low density PETN powder. In a detonation system using a combination of low and high density powders, an apparent center of initiation (COI) analysis of streak data has yielded a surprisingly similar result. This data suggested that a compaction of low density powder to near theoretical maximum density (TMD) may occur before the onset of detonation, which is consistent with work done previously. These experiments show this is not the case and COI analysis reveals a non-ideal initial propagation front. Additionally, data show that although function time increases significantly with decreasing firing voltage, the apparent COI changes very little. This indicates that the detonation criterion is not dependent upon the rate of deflagration, but on a volume of material that must be burned in a confined space to create the critical pressure needed at the compaction front.