Aircraft warning lights  Aircraft warning lights are high-intensity lighting devices attached to tall structures as collision avoidance measures. Such devices make structures more visible to aircraft, and are usually used at night, although they may be used during the day. These lights need to be of sufficient brightness to be visible for miles around the structure. The lights generally come in two forms:    Both types were in use in the United Kingdom until recently. New regulations stipulate the use of red lamps at nighttime only. Xenon flashers are gradually being phased out. In the United States and Canada, there are several types of lights:  Traditionally, red lamps (or beacons) use incandescent filament bulbs. To improve the otherwise quite short lifespan, they are made with a ruggedised design and are run below normal operating power (under-running). A recent development has been the use of arrays of high-power red LEDs in place of incandescent bulbs, which has only been possible since the development of LEDs of sufficient brightness. LED-based lamps have a significantly longer lifespan than incandescent bulbs, thus reducing maintenance costs and increasing reliability. Several manufacturers have also developed medium-intensity white strobes based on LED technology to replace xenon. Xenon flashers, whilst more visually impressive, tend to require frequent replacement and so have become a less favoured option. With the advent of LEDs, white strobes are still somewhat desired. It is common to find structures using white xenon flashers/white strobes during the daytime, and red lights at night. Red lights are commonly found to be used in urban areas, since it is easier for pilots to spot them from above. White strobes (that flash round the clock) may also be used in urban areas. It has been recommended that flashing white strobes should not be used in densely populated areas, as the lights usually merge with background lighting at nighttime, making it difficult for pilots to spot them, aggravating the hazard. In addition, residents near the lit structure will complain of light trespass. In rural areas, red beacons/strobes may also be used during nighttime. White strobes are (sometimes) preferred since they reduce the maintenance cost (i.e. no maintenance of painting, no red side lights) and there are no background lights that would blend with the strobes. There are a medium-intensity white strobe and a high-intensity white strobe. Medium-intensity white strobes are usually used on structures that are between 200–500 feet (61-152.4 meters).