With anti-reflection coating on all surfaces of the element, it heightens the image quality considerably--brings in more light for the brighter picture, and eliminates the strayed beams at the fringe of lens lessening the aberration effects--for the higher and sharper image quality !
It definitely shows the distinction of RAYNOX lens elements from the others which are not coated and improperly treated.

Raynox lens element
Non-coated lens element