Just attach a huge cap across the led, like about 3300uF. Then a resistor to power. Or use 2 resistors from power to led and the cap from the middle junction of the resistors to ground. It will only take a couple of minutes to connect it up and test the results.
I would like dimming on and dimming off.. so like this. or do i need 2 resistors?You're going to need some series resistance between the 12V supply and the capacitor as well, or the charge current of the cap will be limited only be the series resistance of the power supply IE very large. The resistance you need will depend on the actual power supply and LED you're using. A diode in series with the +12V lead will allow instant on and a dimming effect when it turns off.
yep thanks. that is what is was thinking. I'll be trying the one first.Woops, apparently I'm blind =P Sorry that was stupid.
Looks like the lower one is better. The upper one has 1200ohms in series with the power supply, the lower one has 600 from the power supply and 600 from the cap.