To understand what a beam angle is, we need to understand what a beam is.
A beam of light is all within a boundary, with light inside and no light outside the boundary.In general, the light source cannot be infinite, and the light emanating from the light source or luminaire is divergent (except for spotlights that emit parallel light) and does not fill the entire space. Even incandescent bulbs, which are spherical, have a dead end at the cap (the filament is full of light, but the bulb has a cap to block light). So, from the light source or light glow, the place where the light shines is a certain range. Viewed from the tangent plane of the hyperoptical axis, the angle formed by the boundary line of the light range is the actual beam Angle. From a physical point of view, it's the Angle from a boundary that has light to no light at all.
The definition of beam angle is also different in different regions of the world.CIE Europe defines the angle of light beam as the angle between the two sides when the light intensity reaches 50% of the normal light intensity.The International Illuminative Institute (IES USA) stipulates that the Angle formed by the light intensity reaches 10% of the normal light intensity is the beam angle.As you can see, the definitions of the two institutions are quite different. Therefore, the beam angle defined in the standard is not the beam Angle of the actual light source or lamp, but a kind of artificial definition from their own consideration.
The beam Angle reflected on the illuminated wall is spot size and light intensity. If same illuminant is applied in the reflector of different Angle, beam angle is bigger, central light intensity is smaller, light spot is bigger. Applied in indirect lighting principle is the same, the smaller the beam angle, the greater the ambient light intensity, the worse the scattering effect.Generally speaking, narrow beam: beam Angle <20 degrees; Medium beam: beam Angle 20~40 degrees, wide beam: beam Angle >40 degrees.
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Post time: May-07-2022
