Definition
A small kit of replacement light bulbs carried in the airplane for the cockpit and cabin lighting systems, used to replace bulbs that burn out — particularly those needed for instrument, panel, or position lights during night operations.
Plain English
A set of spare light bulbs kept in the airplane so a pilot can swap one in if a cockpit or aircraft light burns out.
Context Anchor
Seen in night flying preparation, especially when checking equipment before an approach or landing after dark.
Why Pilots Care
Maintains required lighting for night operations and prevents a lighting failure from becoming a safety or regulatory issue.
Intuition Check
Do not read this as extra lighting to use in flight. It means replacement bulbs kept available in case an installed bulb burns out.
Example Sentence 1
Before the night cross-country, the pilot checked the spare bulb supply in the glovebox to make sure replacements were available for the panel lights.
Example Sentence 2
During the approach briefing the instructor reminded the student to confirm the spare bulb supply was aboard in case an instrument light failed.