Ever notice that in TV land, people rarely use a light switch?
It doesn't matter which room of a house the character(s) currently occupy; when they move to another room, the lights are already on. And when they leave a room, the lights stay on. Sometimes, characters will even arrive home after a night out, and the lights in the house are already on. The only time the lights go out is when everyone goes to bed, or when darkness is essential to the scene (for instance, an allegedly amusing "fumbling about in the dark" sequence, or to facilitate The Reveal). Or, if a character does turn out the lights upon leaving a room, it's usually symbolic.
Most common in Sit Coms and Soap Operas, where it can be externally justified by the fact that, since such shows often employ Three Wall Sets depicting an "open" architecture, they utilize shared lighting rigs. Further, as anyone who has ever used a klieg light can tell you, big studio lights don't flick on and off in the same manner as 60-watt bulbs; they require long periods of warm-up and cool-down, and turning them on and off during a shoot could be distracting.
Furthermore, these sets will typically feature numerous practical lights (table/floor lamps, sconces, etc). No matter how many such lamps are present, every last one will be burning, day or night. This could be seen as perhaps an attempt to justify the amount of illumination the studio lights are pumping out. However, this trope is also present in animation, where such things ought not to matter.
One of the few times this trope gets a mention is the Christmas Episode, where there are so many more lights than usual that someone will feel the need to, er... hang a lampshade.
Of course, if they ever do switch off the lights, it's not like it gets dark anyway.
See also Law of Conservation of Detail.
- How I Met Your Mother lampshades this in the Christmas Episode variety in "How Lily Stole Christmas". After seeing Lily's "winter wonderland" decorations, Marshal first says how amazing the are followed by "And thank God we don't pay for utilities."
- A Two and a Half Men episode restored some comedy after a dramatic scene: Charlie, exhausted from the drama, turns out the light and climbs up to bed. Then, the camera pans to reveal the rest of the family, still at the dinner table, wondering what just happened.
- Stargate Atlantis routinely displays the entire city lit up despite only having a few hundred people on it, and despite the fact that looking for new ZPM's to power the city is a regular plot driver. It may simply be a scale thing, though. Each ZPM has enough power to open a wormhole to another galaxy, and they have Naquadah reactors with them (which are basically enhanced miniature nuclear reactors). It may just be that turning off the lights to conserve energy for whichever critical system keep draining these would be like turning off a faucet to save the water you need to keep Niagara Falls thundering...
- Lampshaded in an episode of Friends, after Joey sees how big the electric is, he quickly turns off the lights.
- Lampshaded in Married... with Children when Al asked his family why they need to have all the lights on.
- The Big Bang Theory used this in much the same way as the Two and a Half Men reference above. Penny is forced to sleep on Leonard and Sheldon's couch for the night and they all go off to sleep, turning out the lights. Cue the camera panning over to Raj who is left standing bewildered in the darkened kitchen holding a sandwich.
- In Christmas Episodes of Home Improvement, Tim is always shown to be competing to have the best light display in the neighborhood. This usually results in him using so many lights that his house becomes a navigation hazard to passing airplanes. And while his wife may sometimes criticize him about getting overzealous, the electric bill is never brought up. (Then again, the writers glossed over a lot of other questions about money, so at least they're being consistent.)
- Justified and lampshaded in Space Quest Space Quest VI Roger Wilco In The Spinal Frontier. Examining one of the activated lamps in the laboratory will have the narrator comment that the light has a motion detector that automatically turns on when someone enters the room, implying that it turns off when we don't see it. He then adds that it was also cheaper to animate that way.
- Lampshaded in some of the audio commentaries of American Dad! DVDs, where members of the production staff complain about a table lamp that seems to be left on permanently during the day. Remember, this is an animated show we're talking about.
- The Fairly OddParents: "Electric bills are for squares! Like pants!"
- Mission: Magic!: Baron Borealis, Count Celestra, and Madam Marquee are three rivals in "The Land of Lights" who continually vie to create the brightest light display in order to become that land's ruler.