Mysterious LED light triangle relationship
First, the beam angle
Beam angle refers to the angle between two directions in which the luminous intensity is equal to 50% of the maximum intensity on a plane of the vertical beam centerline.
This parameter is commonly used to measure the light intensity distribution of reflective light sources, spotlights, and downlights with narrow angles.
The point of doubt: the beam angle does not refer to the full beam inclusion angle, so the spot that is shot cannot be the angle between the line from the center of the lamp to the outer edge of the spot and the line from the center of the lamp to the center point of the spot.
Advanced: Is it tested with a illuminometer, and the point where 50% illuminance is 50% direct? The answer is: NO! According to the cosine law and the inverse square law, under ideal conditions, the illuminance value Ep of a point where 50% of the light is directly incident should be:
In addition: outdoor lighting often makes the acceptance angle of 1/10 peak light intensity the beam angle of the luminaire.
Second, the shading angle (protection angle shielding angle)
The shielding angle of the luminaire refers to the angle between the line connecting the edge of the light source and the edge of the opening of the luminaire.
Third, the cut angle
Note: The cut-off angle of the fixture is often confused with the shading angle, but the difference is a thousand miles, which is actually the corner of the shading angle. I am too lazy to take pictures, but I will not talk nonsense. I will understand the above picture.
The shading angle and the cut-off angle, which are commonly used to control the glare of the luminaire, are necessary parameters for measuring the visual comfort of the luminosity distribution of the luminaire. Outdoor street lights directly use the cut-off angle to measure the glare level of the fixture.
From the figure we can see that the light of the luminaire, in addition to the direct light source may cause glare, the reflected light on the surface of the lamp cavity material may also cause glare. In addition, the overall brightness of the surface of the luminaire may also cause glare on the surface of indoor materials, especially computers.
In general, light environment glare control is a systems engineering. Just looking at the protection angle is obviously not enough, and now many lighting designers use the beam angle to measure the glare control of the luminaire, which is a bit simple and rude. If you have the conditions, you should still look at the light distribution curve of the luminaire.