Cadillac 1996 DeVille Owner's Manual page 109

Mirrors
Electrochromic DaylNight Rearview Mirror
Your Cadillac has an electrochromic day/night
rearview mirror.
This mirror automatically changes to reduce glare from
'
headlamps behind you. A photocell on the back of the
mirror senses when it is becoming dark outside. Another
photocell built into the mirror surface senses when
headlamps are behind you.
At night, when the glare is too high, the mirror will
gradually darken
to
reduce glare (this change may take a
few seconds). The mirror will return to its clear daytime
state when the glare is reduced.