squeak-
“A Little Light Thinking”
Correct!
The switches are A, B, C and D
Turn on A and B and leave them on for five minutes so the bulbs (including the bases) get good and hot.
Then turn off B, turn on C and immediately go into the “light” room.
The results will be:
A=on,hot
B=off,hot
C=on,slightly warm
D=off,cool
Dr. Pepper-
The “game show” puzzle was so counterintuitive that I refused to believe it until actually trying it out myself.