define lightweight? as in maximum weight u r wanting?
most of the lighter wheels i have seen while havin a look around a few websites r around 13-16lb with the majority around 20lb+
A lightweight wheel can be from 5kg for a 15inch wheel, on top of wheels weight you have the tyre weight. We have Ats Dtc wheels in 15inch size they weigh 5.7kg (i wasn't bothered about weight just liked the look of these wheels)
Oh and these wheels with tyre weigh 18kg