Plain English Meaning

Lights fitted to tall objects on the ground so pilots can see them and avoid hitting them, especially at night or in poor visibility.

Full Definition

Lights placed on tall structures — such as towers, buildings, antennas, smokestacks, and wind turbines — to make those structures visible to pilots at night and in low-visibility conditions. They are typically red (steady-burning or flashing) or high-intensity white (flashing), and may be installed singly, in clusters, or in vertical groups depending on the height and shape of the structure.

Context Anchor

Pilots encounter obstruction lights around airports, along routes, and near tall structures when scanning outside the aircraft, especially during night operations.

Derivation

‘Obstruction’ comes from the Latin obstructus, meaning ‘ up’ or ‘standing in the way.’ In , an obstruction is anything that stands in the way of safe — so an is simply a marking such a .