I reckon if I get some perspex sheet and polish the edges, any light that gets inside the sheet, should bounce around inside of the polished surface. If I then roughen the surface on one face side, the light should 'escape' and give an illuminated surface on which I can put opaque letters to be visible day and night. The question is how to get the light into the perspex. I'm thinking of a series of drilled holes into the top edge with white LEDs stuck in. The drilled holes will have a rougher finish and so the light should enter reasonably efficiently.
Does this sound viable??