There are two main hazards present when trying to get a clean plate from a dishwasher. First, clean plates may appear dirty if patterned or stained; and second, dirty plates can appear clean if not obviously soiled.
This system would work as follows: The indicator shows "DIRTY," until the washing cycle is complete. At the end thereof, it changes to display "CLEAN." Once all dishes have been removed, it changes to "EMPTY." This ensures that dirty dishes are not mixed in with clean, or accidentally removed without washing.-- Alx_xlA, Feb 04 2011random, halfbakery