Given identical barrel lengths, the 1187 light contour barrel shave about a half a pound off the weight.
The chambers, bores and chokes between the standard weight and light contour barrels are the same (excepting the factory backbored trap barrel).
The only difference is in the exterior of the barrels. The standard and light contour barrels are exactly the same out to approximately 4" or so in front of the receiver. From there, the light contour barrel tapers down in diameter. Then, just before the choke tube area, it tapers back up to the standard dimensions. The rib is different in height of its posts to compensate, but the rib top is at the same height.
The light contour barrel definitely changes the balance of the gun. It's nice to carry in the field, shedding an extra half pound of weight. As for recoil, not really noticeable until you start using very heavy loads. The lighter barrels swing much easier. I prefer a standard weight barrel or trap barrel for trap, because it swings more steady and slowly. The light contour barrel is much better suited for sporting clays, because you can easily change direction for the second clay. You can also jink the barrel around more easily in the field when upland birds suddenly change direction.
Some light contour barrel will cycle loads that are slightly lighter than standard weight barrels. Others are equal. It may be that the gas ports on some light contour barrels are slightly larger, or some standard barrels have slightly smaller gas ports. This is because light contour barrel appeal more for those shooting lighter loads, like some target shooters and upland hunters, while the heavier barrel appeal more for duck and geese hunters. In my case, my light contour barrel will cycle loads 1/4 dram lighter than most of my standard barrels. One standard barrel will cycle the same as the light contour barrel.
Light contour barrels cannot be backbored. The barrel is too thin to allow this. However, they can have their forcing cones lengthened, because they are exactly the same in that area as the standard barrels.
Standard barrels will not fit in a light contour barrel's forend, unless the barrel channel is opened up.
From the factory, no light contour barrels came in camo finish. Again this has to do with the type of hunting done. Camo finish appeals more to those using heavy loads, like duck, goose and turkey hunters.
Light contour target barrels, like skeet and sporting clays, are set up to cycle lighter loads than even the field light contour barrels. But they lack a gas compensation system, and cannot be used with heavier field loads.
The 1187 trap barrel has a standard weight barrel contour, but it is factory backbored. This saves a little weight but not as much as the light contour barrel. It's still a heavy barrel. And it is set up for light loads, not the heavier field loads. As far as I know, no light contour trap barrel was made for the 1187, though the late model 1100 trap guns used a light contour trap barrel that was not backbored.