Definition
Light whose rays have been made parallel, so the beam neither spreads outward nor converges to a point as it travels. Collimated light is produced by placing a light source at the focal point of a lens or mirror, which causes the emerging rays to leave on parallel paths.
Plain English
Light that has been straightened out so all its rays travel side by side in the same direction, instead of fanning outward like a normal flashlight beam.
Context Anchor
Seen in discussions of head-up displays, flight simulators, and other cockpit optical displays that are meant to be viewed while the pilot is also looking outside.
Derivation
From the Latin collimare, an alteration of collineare, meaning 'to align' or 'to bring into a straight line.' The same root sits behind the word 'line.' It captures the idea exactly: the rays are brought into line with each other.
Why Pilots Care
Collimated light in displays allows the pilot to see information at a distance focus matching the outside view, reducing eye strain and improving safety during instrument or night flying.
Analogy
A laser pointer is a familiar example of light that stays in a tight, straight path. Collimated light in a cockpit display is used for a different purpose, but the idea of lined-up light rays is similar.
Grounding Statement
Picture a flashlight beam that, instead of widening on a wall across the room, stays the same width no matter how far away the wall is. That is collimated light.
Intuition Check
Collimated does not mean simply brighter or clearer. It means the light rays are lined up so the image appears far away.
Example Sentence 1
The HUD uses collimated light so the airspeed and altitude symbols appear to float at the same distance as the runway ahead.
Example Sentence 2
Instrument lighting uses collimated light to keep the panel bright and readable without glare that spreads into the pilot's view.