From SCP: Secret Laboratory Public Beta Official Wiki
Used to display access levels of a Keycard. To make things easier. By default, all tiers are darken, one must put "CC2 = " to make a tier light up (MUST BE LEFT BLANK). For Containment and Amories Tiers, telling a higher tier to light up will automatically do the same for lower tiers. This does have the funny side effect where you can use an override so AA3 can be lighten up but AA1 stays darken.
Example:
Funny override I found while testing:
