Electronics > Electronics

LED question

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hazzer123:
Pretty straight forward question :)

How long, after I apply voltage to an LED, does it take to light up? How long after i take it away will the light stop? is it a gradual increase in brightness when powered on?

Thanks

ed1380:
fast enough so that our eyes think it's instant.

hazzer123:
Yeh but not exactly instant thought :D

Any ideas how long?

dunk:
so i don't know this for a fact but i've always presumed very very quickly.

infared LEDs are capable of operating at a frequency of 40kHz (in TV remote controlls for example) so an IR LED can switch on and off again within 1/40,000th of a second.

i don't know if standard visual spectrum LEDs are optimised to operate quite that quickly but i think it's safe to assume they light up in a few thousandths of a second.

dunk.

Brandon121233:
the human eye has trouble distinguishing things at about 20 hertz, or frames per second. So if you mean how fast the eye could detect it flashing, then the LED can go a lot faster than what you can detect, it will look like it is constantly on to you.

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