Eli5: Why does a camera have to flash and time it perfectly when it takes a picture? Can’t the light just stay on?
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In old cameras they used a very bright [Xenon strobe lamp](https://en.wikipedia.org/wiki/Flashtube) which is *very* bright (far brighter than a traditional filament lamp could manage) but can’t be sustained, certainly not from a battery supply – so they just trigger it as the shutter opens which is actually very easy.
In modern phone cameras, the LED that’s the flash can stay on for a while longer but at maximum brightness it will get hot very quickly – often the “flash” uses a far brighter level (more power) than the LED could actually survive for more than a second or so without overheating & burning out.
In “torch” mode the LED is powered at a lower level so can stay lit without overheating.
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