Definition
An indicator or warning light fitted with a built-in switch that completes a circuit through the bulb when the lens is pressed inward. Pressing the lens energizes the bulb directly so the pilot can confirm the bulb is good before relying on it to indicate a system condition.
Plain English
A warning light you can press to check that the bulb still works. If it lights up when you push it, you know the bulb isn't burned out, so you can trust it later when it comes on for a real reason.
Context Anchor
Seen on annunciator panels, warning lights, caution lights, and system status panels during preflight or maintenance checks.
Why Pilots Care
Confirms that critical warning lights will actually illuminate if a system fault occurs, preventing missed alerts.
Intuition Check
Do not assume pressing the light proves the whole aircraft system is working correctly. It mainly proves that the light and its test path can make the indicator come on.
Example Sentence 1
During the preflight check, the pilot pressed each annunciator lens to confirm the press-to-test lights all illuminated.
Example Sentence 2
A failed press-to-test light on the oil-pressure warning prompted the mechanic to replace the bulb before the next flight.