What does a flash on a camera do?

Old flash bulbs contained a lot of jumbled tungsten, zirconium or aluminum wire housed in an oxygen atmosphere that was rapidly burnt when the shutter was clicked. Early amateur cameras supplied the current by battery. Later, simple point and shoot cameras like the Kodak Instamatic used something other than a battery (probably a piezoelectric device like a barbecue starter, but I'm just guessing). The bulbs were blue coated to balance the light for color film, and some contained a blue dot to indicate the oxygen had not leaked out and been replaced by air. If an air contaminated bulb was used, it usually exploded.

Some cave photographers prefer the flash bulb to an electronic strobe, claiming the quantity of light output is superior. However, bulbs are getting harder to find.