I originally built the displays for an old timey calculator made from vacuum tubes and relays. I wanted a vintage look for the machine but nice big and clear digits to display the numbers.
This calculator uses rotary switches to input numbers to be add/subtracted. A s you can see even in a very brightly lit room the digits are clear and easy to read(despite my poor photography) This picture shows the input numbers, the = sign and equals and the resulting solution.
I then built this all relay version of the calculator:
This shows the same except the solution contains 2 digits.
Both of these machines are using line voltage(120vac) rectified and filtered(170VDC) to power the digits.