What is the beam angle? What is the shading angle?

According to the definition of JGJ/T 119-2008, the beam angle is the angle between the two radial diameters of the luminous intensity curve expressed in polar coordinates on a given plane. The illuminance intensity value of the radial diameter is usually equal to a maximum of 10% or 50% of the luminescence intensity. As shown, at an peak intensity of 50%, the angle is 2x34°.

The beam angle is generally for the luminaire, but it can also be used for the reflection type source, but it is not clear in this standard which case uses 10% and in which case 50%.

In practical applications, the CIE (International Commission on Illumination) recommends a beam angle of 50% of the maximum light intensity; and IES (North American Lighting Engineering Association) recommends a beam angle of 10% of the maximum light intensity. For non-fully symmetric luminaires, such as in C = 0 ° (and) in the cross section of γ = 0 °, the angle of the beam with a light intensity of 10% of the peak intensity may be different, ie the lateral and longitudinal directions of the luminaire The beam angles may be different.

The beam angle of the fixture reacts to the spot and brightness on the illuminated wall. If the same light source is applied to reflectors of different angles, the larger the beam angle, the smaller the center intensity and the larger the spot size. The principle is also the same when applied to indirect illumination. The smaller the beam angle, the smaller the ambient light intensity and the worse the scattering effect. In addition, the beam angle of the luminaire is also affected by the relative position of the light source and the lamp cover.

In addition, when the angle contained in the direction in which the luminous intensity is equal to 1/2 of the peak intensity is defined as the beam angle, in general, the beam angle of the narrow beam is less than 20°; the beam angle of the medium beam is 20° to 40°, and the width is wide. The beam angle of the beam will be greater than 40°.

What is the shielding angle?

The shading angle is the complementary angle of the intercept angle. So what is the cut-off angle? The intercept angle is the angle between the vertical axis of the luminaire and the line of sight of the illuminant where the high brightness is not visible. Especially in road lighting, the cut-off angle is an important indicator to limit glare.

Beam angle application

In practice, different beam angles have different applications. For example, a narrow beam is easy to produce a high key illumination factor, and its strong contrast between light and dark gives a strong visual impact. It can catch people's eyes in the first time, but too high contrast will make the observers invisible. The details of the object, and the spot is too small, will also cause the object to be illuminated. Therefore, in practical applications, factors such as the distance, direction, and ambient brightness of the lamp should be considered.