The plane angle of diffusion, often referred to simply as the diffusion angle or beam angle in practical terms, is a specific measure used to describe how light spreads from a luminaire.
Understanding the Plane Angle of Diffusion
According to DIN 5037, Sheet 1, the plane angle of diffusion is defined as a plane angle that describes the rotation-symmetrical light distribution of a spot or flood.
Here's a breakdown of its key characteristics based on the standard:
- Purpose: It quantifies the spread of light, particularly for light sources like spotlights or floodlights that emit light in a cone shape.
- Formation: It is formed by two beam angles located within a single plane. These two beam angles must have equal Luminous Intensity.
- Condition: The luminous intensity within this angle of diffusion must be higher than the luminous intensity selected as the reference point for defining the angle. This ensures the angle captures the significant, brighter portion of the light output.
Essentially, it's a standardized way to measure the effective beam width of a light source at a certain intensity level.
How it Characterizes Light Distribution
The size of the diffusion angle directly tells you how focused or spread out the light is:
- Narrow Diffusion Angle: Indicates a spotlight effect, concentrating light intensely over a small area. (e.g., < 10°)
- Wide Diffusion Angle: Indicates a floodlight effect, spreading light more broadly over a larger area. (e.g., > 25°)
This angle is crucial for lighting designers to predict coverage and intensity on surfaces, ensuring appropriate illumination for specific tasks or environments, whether it's highlighting an object or general area lighting.
Examples:
- A museum might use lights with narrow diffusion angles to focus precisely on artwork.
- An outdoor security light might use a wide diffusion angle to cover a large yard.
Understanding the diffusion angle, or plane angle of diffusion, is fundamental in selecting the right lighting fixture for a desired effect and coverage area.
