dim on dim off circuit?

i am putting LEDs in my headlights, and i am trying to figure out how to make a circuit that will dim them on, wait 5 seconds,then dim them off, continuously until the circuit power is cut when the relay is energized by the car coming on. this dimming is similar to a newer iMac or Emac, when it is in sleep mode, if that makes it easier. i only know how to make it dim down using a capacitor, but i dont know how to delay it or dim it up. any advice would be extremely helpful.

If you wanted the to blink dei makes a great little module for that It has 5 lights that is triggered by the ground when the alarm is armed. you may be able to use that in some way for your application hope that helps

You need to do some research in to pulse width modulation.  That is the best way to dim LEDs on and off.Kevin Pierson

ok, so i thought about the pulse width modulation, and ive had trouble figuring out how to do it standalone, without a pc. so i know that if i rig up a capacitor, that the light will dim off as the capacitor drains. but how to make it get gradually brighter when the power comes on is my question....