How can i get Indications unvisible when not illuminated?
i have a question moving around my head for weeks now, maybe someone can help.
There a parts in the Cockpit of an Airliner, where Indications may only be visible when not illuminated. Examples are Korrys, or Indications like "Alt" "Hdg "Trk" on the A320 FCU just above the 7-Segment-Digits.
So the question is, how can i get those indications visible when i light them, but completly unvisible, when not lighted?
Possible solutions, which came up to me:
1. Sheet of white film, on top of which i put a sheet of black film with cut-outs in form of the letters. Now i put a very thin black film on top of this, which will allow a strong light to shine through it, but not the normal light from the cockpit environment.
2. Same thing just with lacquer. Laser-engrave the black part and than overspray with a very thin coating of black again.
Anyone tryed those things in the past or has a much better idea?
Thanks for help!