URGENT, LED explainantion

Guys,
can anyone help me this question ?

"With the aid of a sketch, describe briefly how the intensity of light from an LED can be modulated directly."


Regards,
Linspire

You can directly modulate or interrupt the current through any LED. No sketch is needed, simply modulate or control LED current.
You can also interrupt the LED light output mechanically- in optical experiments you can use a rotating perforated disk, or, a small hole covered with a vibrating screen.

Can you show me some videos or figure for your explainantion optical experiments ?
I'm curious about it.

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Thank you , E Kafeman.