Diameter
A fixture should feel intentional without crowding surrounding architecture. Compare the listed diameter with the ceiling plane and major furniture below it. In a corridor, confirm door and cabinet clearance as well as the visual footprint.
Height and profile
Overall height matters most in rooms with lower ceilings. Flush mounts sit closest to the ceiling; semi-flush and suspended forms need more vertical clearance. Product dimensions are the ordering reference even when gallery images show multiple sizes.
Fan-light clearance
For fan lights, use the published overall span and height, maintain safe clearance from walls and cabinetry, and install only to a fan-rated box with suitable structure.