The Dually and D2 are housed in the same cast aluminum housing and have the same shape and profile. The difference is what's inside. The Dually uses our Hybrid Optics System in a 4-LED configuration which comes in either Spot or Flood options. It produces 1,568 lumens at only 15.8 watts and 1.1 amps. To put that in perspective, it uses less power than it takes to use your turn signal. The D2 has 6 LED's that utilize our Specter Optics System, which comes in either Driving or Wide configurations. It produces 3,096 lumens and uses only 34.5 watts and 2.5 amps. The D2, with its driving beam, produces the perfect combination of distance and width for lighting up the road or water in front of you.