Definition
A light, or group of lights, mounted on a tall structure to make it visible to pilots at night or in low visibility, marking the structure as a hazard to flight. Obstruction lights are typically red (steady or flashing) or high-intensity white, and are placed on objects such as towers, tall buildings, cranes, wind turbines, and antennas that penetrate navigable airspace.
Plain English
A warning light fitted to a tall object so pilots can see and avoid it, especially at night.
Context Anchor
Pilots encounter obstruction lights on tall objects near airports, along routes, and around construction or antenna sites.
Derivation
From the Latin obstruere, meaning 'to block' or 'build against.' An obstruction is something that gets in the way — here, something tall enough to get in the way of an aircraft. The light makes that obstruction visible.
Why Pilots Care
Helps prevent mid-air collisions with man-made or natural obstacles during night, IMC, or low-level flight.
Analogy
Like the blinking red lights on radio towers visible from a highway at night, but positioned and sized for pilots to spot from the air.
Intuition Check
An obstruction light is not a runway light or a light that shows where to go. It marks something to avoid.
Example Sentence 1
On the night cross-country, the flashing red obstruction lights on the radio tower were visible from several miles out.
Example Sentence 2
During the night cross-country, the obstruction lights on the wind farm were visible well before the aircraft reached them.