It’s likely the only time you really notice one of your neighborhood broadcast and cell towers is at night when they’re lit up with conspicuous bright red lights. Those lights help pilots see the huge metal structures that can reach 1,000 feet into the air — but they can spell disaster for birds.

A Steady Red light signal on the ground means the same to an airplane as a red traffic light means to a car. RED means STOP. The steady red light means the aircraft must stop immediately. The controller wants the pilot to hold their position.

Airplanes are designed with red and green navigation because it’s the same configuration used in boats. During the 19th century, mariners discovered that adding red and green flashing lights to their boats lowered the risk of collisions. Therefore, aviation experts applied this same configuration to airplanes.

Buildings and towers with a height of more than 35m are also fitted with red lights. These are called aircraft warning lights. Now you know why red light are used. In the US, any tower over 200 feet requires a signal light per FAA regulations to protect planes flying by who might not see it.

200 feet

Television- and radio-transmitting towers are among the tallest and most fragile structures built, with some up to 2,000 ft. (609.60 m) in height.

Walk a distance away from the tower until you can see the top of the tower through the straw. Since you are sighting the top of the tower at a 45-degree angle, your distance from the tower is equal to the height of the tower. Measure your distance from the tower and you know its height.

Aircraft warning lights are high-intensity lighting devices attached to tall structures to increase visibility to climbing and descending aircraft. Such devices prevent aircraft from collisions, and are usually used at night, although they may be used during the day.

Strobe lights are flashing white lights on the furthest left, right and, on larger aircraft and some smaller ones, back points of an aircraft. They are the brightest lights on the aircraft, and are used to signal that an aircraft is entering or approaching an active runway, or for visibility in dark, clear sky.

Since not all workers leave at the same time, no one will be left in the dark if the lights remain on as the other workers leave the room. There is also a smaller risk to the personal safety of the workers in the building if the lights remain on, because no one has to stumble over chairs to turn them on.

What’s more, some businesses intentionally leave lights on for security purposes (though the jury is out on whether this actually reduces crime). Cleaning crews remain in buildings well into the night, and more and more people are working nontraditional hours.

Advertising. Instead, many retail locations appear to leave lights on at night (especially lights highlighting product displays) in order to advertise, both the existence of the store and the products for sale within.

Large buildings have a number of reasons to leave some of the lights on. Few of the reasons are: As per regulations, for safety reasons spaces inside a building especially egress paths always need to be lit so that it would help in easy evacuation during an emergency.

Electricity was cheaper and architects thought the buildings looked better illuminated. Times have changed, but even today in large offices lights are kept on for the cleaning crews who come in at night. Also lights are kept on for late workers.

Con Edison, the utility that provides power to New York, estimated that 5,200 megawatt-hours of electricity keep Manhattan lit overnight. “The reality of this is, about 99 percent of those lights need to be on at night,” said John Catuogno, the director of resource planning and forecasting at the utility.

Many towers serve as office space, but others are residential buildings. In both kinds of skyscrapers, emergency exits usually stay lit — even when many New Yorkers are sleeping. Fire codes also require a minimum lighting condition, especially around stairs and fire exits, even (or especially) at night.