Standard junction boxes, designed to be nailed to ceiling joists, are appropriate for very lightweight lighting fixtures, such as flush-mounted fixtures.
Medium Weight Fixtures
Junction boxes with expanding devices on the sides and Madison hangers are generally recommended for use with lighting fixtures less than 50 pounds. This recommendation results because of the relatively small area to which they anchor.
Most chandeliers and ceiling fans are too heavy for this type of hanger, although they are appropriate for some pendant light fixtures. Don't over-tighten the expanding device; the tension it puts on the joists can cause nail pops in the drywall below.
Chandeliers range in size but are generally considered heavy to very heavy. You should secure hanging light fixtures, such as chandeliers and ceiling fans, to the house's permanent structure.
You should suspend lighting fixtures weighing between 50 and 100 pounds with a mounting bar that has an expanding feature. This expanding feature allows you to tighten the bar between ceiling joists.
Remember to leave enough clearance to attach an electrical box to the bar. The bottom of the box should be flush with the ceiling surface.