It’s good to mix it up every now and again to stimulate muscle confusion. In this confused state, the muscles feel challenged and as a result, are forced to change and adapt to step up to the challenges, therefore, they become more responsive in producing results for fat-burn, strengthening, and developing lean muscle definition.
But as a general guideline: you can’t exactly burn a ton of calories during the process of lifting light weights in steady sets, but going heavier does melt more calories, especially when you work at an uncomfortable intensity that will produce the “after-burn” effect. Using heavy dumbbells triggers more fat-burning hormones, which fire up your metabolism for hours after the workout (creating the “after-burn” effect).
Aim for 3-5 sets of 8-12 reps at a weight that makes the last 2 reps tough to complete — tough enough you almost have to hold back from letting out a little growl. ;)