Definition
Light made up of waves of many different wavelengths and phases, traveling in many directions at once. Ordinary light from the sun, a flashlight, or a landing light is incoherent. It is the opposite of coherent light, which has waves of a single wavelength all in step with each other (as produced by a laser).
Plain English
Normal, everyday light. The waves are mixed together at random rather than lined up neatly. A landing light or a household bulb gives off this kind of light.
Context Anchor
Seen in aircraft lighting, optical equipment, and avionics discussions when comparing ordinary light sources with laser light.
Derivation
Incoherent comes from the Latin in- (not) and cohaerere (to stick together). The light waves do not stick together in step — they are out of sync with one another.
Why Pilots Care
The term helps separate ordinary light from laser light in equipment descriptions, warnings, and maintenance information. That matters because organized laser light can behave very differently from normal lamp light.
Analogy
Think of a crowd of people all walking in different directions at different speeds — that is incoherent light. A marching band stepping in unison would be coherent light.
Intuition Check
Do not read incoherent here as “confused speech” or “not understandable.” In optics, it means the light waves are not lined up in a steady, organized timing pattern.
Example Sentence 1
A standard aircraft landing light produces incoherent light, scattering in many directions to illuminate the runway.
Example Sentence 2
Unlike a laser, the incoherent light from the taxi lights gives even illumination without creating bright spots or interference patterns.