The light on a personal flotation device on an OSV must be replaced __________.

Correct Answer: Option C — when it is no longer serviceable

46 CFR 133.70 dictates that PFD lights must be maintained in operational condition. While specific replacement intervals for batteries are often manufacturer-dependent, the regulatory requirement is that the light must be replaced when it is no longer serviceable, ensuring reliability during emergency abandonment or man-overboard situations.