We are planning on using an acrylic plate as screen on which the letters are projected from the back. I have ordered several samples of white acrylic with varying optical transmission. Unfortunately, the outline of the letters is always blurred on the acrylic sheets. This is because the light is diffused too much within the plates which are rather thick (2-3 mm). Therefore, the current plan is to use a thin semitransparent foil (similar to the previous version of our clock) which will then be attached to a transparent sheet of acrylic. As can be seen in the last picture, the projection has a sharp outline on the foil.