Good question. Please see my detailed discussion of the matter here. Nutshell version: there's a mountain of unsafe garbage on the market, but there are (finally) the first few legitimate retrofits: these to replace 1034 or 1157 in red brake/tail lights, and these to replace 1076, 1141, or 1156 in reversing (back-up) lights.
If you use these in your brake/tail lights, you will need to swap in this turn signal flasher.
