The home made swirl spotters as mentioned are good. Either make one yourself or see if anyone on DW is selling them.
Alternatively, a little hand held LED torch can be useful on darker colours.
For bigger portable lights, halogen are ok but metal halide is the way to go really. Search on eBay and there are plenty for sale. 150w will be plenty and show up pretty much all defects on any paint colour (including silvers/whites)