When the power goes out, the power loss cascades across the entire strip. When it reaches the Luxor, the beam from the top of the pyramid shuts down. The light from the beam is then seen to disappear, starting at the top of the beam, and ending at the pyramid. This is impossible, as the light originates from the pyramid, and thus the light would disappear in an upward direction.
There is a city-wide blackout and the elevators, cameras, and automatic door locks stop working, yet a bank of slot machines continues to operate in the Montecito. Any Las Vegas casino would be required to have generators that would power essential safety systems at a minimum.