Some articles on flashbulbs, flashbulb:

Flashgun - Types of Flash - Flashbulbs - Flashcubes, Magicubes and Flipflash
... their Instamatic camera line by replacing the individual flashbulb technology (used on early Instamatics) with the Flashcube ... consisted of four electrically fired flashbulbs with an integral reflector in a cube-shaped arrangement that allowed taking four images in a row ... Other common flashbulb-based devices were the Flashbar and Flipflash which included ten or so bulbs in a single unit ...