Mount those things down low behind the rear bumper so you get all the light, not just a glare from the light shining off your rear tire and tailgate. I had some Dualies mounted behind the cab and I never used them because the light output sucked when it hit the back of the truck.. I had a "shadow" area 20-30' behind the truck. If you are using them as backup lights put them down low.. and if you are using them as work light mount them on your swingout tire carrier.
Mine where like this.. lots of light output, just in the wrong areas. One time they came in handy was camping and Scott arrived late so I lit up his area to setup his tent... but that area was 50' away from the truck. If they where on the swingout it would have done the same thing.