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unfortunately 2 lamps defective
No surprise....Datasheet says lamp life was 400-600 hours, which is pretty horrible.
These otherwise look like fairly rugged units, so I'm surprised at the short lifetime of the bulbs.
My father worked on aircraft instruments, and bulb life was typically 100,000 hours. LEDs were very slow to replace incandescent bulbs because they lacked sunlight readability in a cockpit environment.