I was just e-mailed back from Heser lights that they don't sell just the replacement bulb asssembly for use as an upgrade because they can't guarantee the bulb without the cooling tube insert in their light housing. Its like the obverse of "Sansabelt Pants" ;you can buy just the belt but you have to buy and wear the pants that come with them. I wrote back that the light I want to upgrade was solid aluminum, effectivly (I think) a cooling tube.