Turing on led and 20 second lader stay off

[missdrew]

@Bjerknez

Arduino for lighting up an led for 20 seconds and turn it off?

That was not your specification.

@Bjerknez

I want the led to fade on after door is opened and stay on for 20 seconds before the the led fades off and stays off

This was your specification, notice the word 'fade'? Turn an LED on, and turn it off after 20 seconds is not the same. On/Off can be done.

And yes, Using the Arduino/ General Electronics section does kind of tell us it's general electronics using an Arduino!