fade on/fade out LED

breadboard with 9V battery, run through a 2.2k resistor to a 1000μF capacitor, which spills into a 220 resistor to an LED.

the capacitor takes time to fill and once it has, it "spills over" and powers the LED. This causes the LED to fade on. When the button is no longer being pressed, the power is cut, but the LED fades off because the capacitor drains over time into the LED until there is no power left.