A lighting system producing a light pattern that is customized in the field by the end user to minimize light pollution. A housing supports a light source that is connected to a power supply. The housing defines an interior chamber. An opaque or low visible light transmissivity shield is bent or formed into a generally tubular shape and is inserted into the chamber surrounding the light source. The shield includes folds, perforations, pre-scoring, grooves, and the like defining sections that can be easily detached to create windows. The windows permit outgoing light to pass while the remaining areas of the shield attenuate or block the outgoing light. The shield includes teeth that engage respective recesses in the housing to prevent rotation of the shield once installed.