An eyepiece includes a viewing region to emit display light out of the eyepiece along an eye-ward direction, an input end peripherally located from the viewing region and configured to receive the display light into the eyepiece, one or more optical elements positioned to direct the display light received into the eyepiece out of the viewing region along the eye-ward direction, a first side through which ambient scene light is received into the eyepiece, a second side out of which the ambient scene light and the display light are passed along the eye-ward direction, and a photo-chromic coating disposed on the first side and the second side, the photo-chromic coating to darken in the presence of UV light.