Now i am sure that most of you know you can buy decent LED replacement bulbs on eBay, that will replace a 21w bulb. However that is not as much fun as building your own units.
Now this is a very simple method using cheap materials. as always i try not to over complicate things,
-4 8mm 0.5w strawhat LED's per light
-a piece of semi-rigid plastic to cut 35mm discs out of (i.e. ABS)
-soldering iron and solder
-drill and drill bits
-small nut and bolt (M4-M6)
-heat shrink sleaving 4mm