I've never found rhyme nor reason as to why some work and some don't.  Best ones I've ever bought came from one of these" sale a day" online sites.  They take 4 D batteries, but they work perfectly.  Got one on the shed I bought in a clearance aisle that has worked great.  Every other motion light I've bought (generally paying retail ... maybe there's a pattern here) has failed.  Sometimes long before I thought it should.