Some water storage tanks have aviation warning lights on them. The FAA regulations require the bulbs to be replaced before they reach what percentage of their normal life expectancy?

• A. 50%
• B. 75%
• C. 90%
• D. 100%

Answer: (B)

Maintaining aviation warning lights requires replacing bulbs before they degrade too much, so the light stays within the required brightness range and remains reliable for aircraft visibility. The lamps have a rated life from the manufacturer, but as they age, their light output drops. Replacing them at 75% of their normal life expectancy gives a safety buffer: you avoid a dimming or failure that could occur near the end of life, while not replacing too early and wasting resources. Waiting until 90% or 100% increases the risk of reduced intensity or outage during service, and 50% is unnecessarily early. That’s why 75% is the best-prescribed threshold.