Can someone please suggest which glue to use to glue opal acrylic letters to a sheet of acrylic, which doesn't hinder the back lighting. As in it allows maximum light through and you can't see glue marks. The job is a dibond panel with the logo cut out and opal 3d letters in the cut out area (which light up from the back light). To fix the letters I'm placing a 1.5mm acrylic sheet to the back of the dibond to allow me to fix the letters to the panel. I don't want any glue marks to hinder the light or to be visible. Thanks for any suggestions!