hi for NPN transistor normally Collector will be connected with Vcc, resistor then LED. and Emitter will be conencted to Vss. So whenever voltage applied to base LED illuminates.
however when Vcc connected to Emitter and Vss to Collector (the rest remains, LED polarity changed) LED illuminates too when there is a base voltage.
any idea? as far i know NPN conducts from C to E only.