Canister has two louvered vents and accommodates halogen or incandescent bulbs with standard medium base. Canister is constructed of drawn steel. 3.5 feet diameter is required . Fixture is installed from top of panel and attached with three screws through adjustable plastic mounting ring , positioned on canister per customer speciticstions (consider overall crown height, panel thickness, etc.). The wire exit side of the canister and are secured by strain-relief bushings. Each fixture can be wired in a series of u to six lights with wire length specified by customer. Select controls section. Please contact the factory assistance with custom designs.