Depending on the fixture, the connections might be able to be made inside the fixture without a junction box. Please read the fixture's installation instructions to see if this is permissible.

Whether or not a junction box is required, heavy fixtures frequently need support in addition to any support a junction box might provide. The best solution is to mount any fixture directly into wall studs whenever possible. If studs are not in the right place, most vanity fixtures can be mounted using hardware like toggle bolts or mollies.

You should find a stud every 16" if the house was built using standard platform framing methods. But if you live in an older house, you might encounter balloon framing or perhaps post-and-beam framing where the dimensions are not at all standard.

For holes larger than the cover plate, you need to patch the wall. Depending on the construction of the house, this could as simple as securing a piece of drywall (and a little "mud" and tape), or a much more complex process using lath and plaster.

Thanks for the reply kurto. The house is less than 10 yrs old and was suppose to be built to a specific code but undoubtedly it wasn't. The hall bath has the boxes not sure why they left them out of the master. Looks like we might be taking down more Sheetrock and adding a brace for the lights. The worst part is that we had just had the inside of the house painted and it is egg shell paint which means no touch up for the wall:( Oh well, the ORB fixture will look so much nicer in the end. Thanks again for your help.

If you're careful where you intend to install the light, shadowing around the base should mask any evidence of touch up. Also, if you feather the paint when you touch it up, chances are it will not even show.

You can buy a device for hanging a fan. It goes into the existing hole (box-sized) and expands to fit between the studs. The box attaches to it with a supplied 'U' bolt/clamp.

If it can hold a 40lb fan, it should hold your light fixture.