Each personal flotation device light on an OSV that has a non-replacement power source must be replaced __________.

Correct Answer: Option D — on or before the expiration date of the power source

46 CFR 133.140 requires that personal flotation device lights with non-replaceable power sources be replaced on or before the manufacturer's expiration date. This ensures the reliability of emergency equipment, as battery degradation over time could otherwise result in a failure to illuminate when needed during a distress situation.