Each day we are asked by client's how large a ceiling medallion should be for their chandelier. So many people think that the medallion should be the same size as their fixture, however this is inconsistant with the original concept of the medallion.
In the 1700's most mansions had light fixtures hanging from chain in very tall rooms with gas or candle flames. As time progressed more moderate homes were built with lower ceilings. Now those gas lights would catch the ceiling on fire, so the solution was the fire rated ceiling medallion usually made from plaster. Of course it had to be larger than the fixture to protect from fire.
The general design rule is that the medallion, a show piece of the room, be larger than the fixture for both asthetics and safety. When the medallion is installed on the ceiling it looks much smaller than it does in hand. This concept of perspective was well know by renaissance artists.
So here is a formula to help you size your medallion.
The concept of PHi is the ancient "Golden Rule" of proportion ratio.
1 - (.618) = (.382) ie 38.2%
So an 18 inch medallion x 1.38 = a 25 inch medallion
That being said no rules rule and something around 25 inch would give you the best proportion. This will give you the best visual effect for your desired design concept. Imperial has the widest and best selection of medallion in variable material to satisfy any design plan.
Martin Richards Design