These are 31mm festoon LED bulbs (also called festoon LED lamps or C5W / DE3175 LED replacements).
LED upgrades for the small tube-shaped “festoon” bulbs commonly used in cars.
Typical applications:
Interior dome / map lights
License plate lights
Door courtesy lights
Trunk / boot lights
Some vanity mirror lights
Description
Left side
Fully assembled 31 mm festoon LEDs with metal end caps. Labeled 31MM-21LED (31 mm long, 21 LED chips).
Right side
Bare LED circuit boards (the same type before the metal end caps are added).
Key features
Blue PCB with multiple yellow SMD LED chips arranged in rows.
Metal contact ends that fit into the standard festoon bulb sockets.
Much brighter and longer-lasting than the original halogen/incandescent festoon bulbs.
Usually available in different color temperatures (cool white, warm white, etc.).