Some tiles have designs engraved on them. Some are traditional and some are modern. Your choice depends on the kind of look you want for your interiors. You can easily install them as they are light in weight by applying any simple construction adhesive. Take care that they are fitted together quite well and the grooves between them are not visible.
You can modify an antique piece of birdcage into an apparatus to hold the light. A modern chandelier lighting will give a classy look.
If you hide the lighting fixture behind the molding, it would have truly a dramatic effect on the tray ceiling.