Let's Make Robots!

LED "reaction time"

I'm thinking of using a bunch of LEDs for a secret project. Here's the catch: they have to be able 'flicker' too quickly for the human eye to see. 

How quickly do LEDs go from off to on? Is there any delay - do they have to 'warm up' like incandescent light bulbs? Realize a half second delay is way too much for the project I have in mind. Are there any fast-acting LEDs out there? Or is it virtually instant, only hindered by the speed of the electrons through the wire?

also, while I'm talking about LEDs, what's the simplest way to control a whole bunch of them? Is there any serial driver that can control a whole bunch (upwards of 32 eventually but 18 for now as proof of concept) of LEDs independently of each other? Bonus points for scalability.

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have you ever connected a led to a PWM signal ( like the ones to control a servo )?

they flick, but you don't see them flick

"typical" human eye won't see above 50Hz, or bellow 20ms, so if you turn them off for, lets say, 10ms, you should be fine


as for controll a bunch of them you can use I2C IO expanders, not sure about 32, but there are some with 16.

Or you can use shift registers in series like the 74x595

thanks, an i2c io expander seems like exactly what I need.

if you want them to flicker faster than the eye can see, then why turn them on at all?

It's not that I want them to flicker faster then the eye can see, I want them to flicker off for a moment so it doesn't interfere with something else... well, it's hard to explain. You'll understand after I finish. 

If you want to turn them on, but not see them, you don't even need power! Jk

I believe most leds will be very fast, muuuch less than half a second. 

if you have their datasheets, it might just be there.

Thanks! I've tried a few datasheets but I haven't found anything.

I thought they were pretty much instant too, but I don't know how fast instant is. I guess I'll just have to experiment with them.