Huuh yeah, from the floor. Standard height of playing surface is 30½" to 31½" inches but that of course may vary especially with garage floors that are sloped toward the door.
My 2¢ ... The higher the light the more even the light across the table. Think of the studio lights used in TV tournaments. With diffuser style like rexus31's you can go higher than 30" because the light source is not in your eyes in your stance. Brunswick, Diamond and AMF only sell/sold diffused lights. An undiffused light may need to be lower so the light doesn't shine in your eyes in your stance.