High voltage power cables, particularly those close to airports, need to be visible day and night. During the day, brightly coloured balls positioned along the length of the cables are sufficient, but during the night, lighting is necessary. These beacons which emit a red glow (the standard colour used in aviation for warning beacons) are used to provide this lighting.
The system is extremely simple, efficient and reliable and is considered the most economically viable solution. Its working principle is attractive because it uses a phenomenon usually considered as a weakness. However a large disadvantage is that it does not work when the line is switched off. It cannot also be used on HVDC powerlines.