system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why did you need to wait for the "green light" on old cameras to use the flash? What was taking so long ?
gpt
The flash bulbs required a large amount of power very quickly in order to produce the flash. The battery in the flash was not capable of delivering that amount of power that fast, so the flash would store a bunch of power in a capacitor which would then deliver it to the bulb for the flash.  Once the capacitor discharged, it took a few seconds to charge up again.

This isn't a big deal anymore, as our batteries are a lot better and our flashes much more power efficient.