Beam Angle

light metric

Definition of Beam Angle

Beam angle is the measurement of how wide the light spreads from a light fixture. It’s usually measured at the angle at which the light beam reaches 50% of its peak intensity.

spot beam angle diagram

A broad beam angle illuminates a wider area with less intense light while a narrower beam angle gives high intensity light to a smaller area.

diagram of the effectiveness of a narrow beam

Using this metric, light sources can be divided into:

Beam angle is an essential metric for optimizing light coverage on your boat and ensuring your navigation lights meet nautical safety standards.

How do you choose light fixtures with the most suitable beam angle for your lighting needs?

Beam Angle Pro Con Lighting Application
Narrow beam angle <45°
  • Focused light good for highlighting details (accent lighting)
  • Beam is concentrated enough to provide greater visibility from a great distance away
  • Areas outside the beam’s center are completely dark
  • Doesn’t illuminate large but proximate areas, such as boat decks
Wide beam angle >45°
  • Clear, even light that leaves no dark areas in a space
  • Allows you to use fewer fixtures as the light spreads wide
  • Only lights proximate areas well
  • Light disperses and dims significantly over a great distance

"Floodlight would work great for a smaller boat deck light. We use it for side lighting for buoys while fishing and it lights the dock up very well when pulling into the stall." Doug D., United States

Example of Beam Angle in a Sentence

"The starboard and port sidelights of a boat should have an unbroken beam angle of 112.5°."

Synonyms: beam spread, radiation angle

Related Terms for Beam Angle