Interpretation and analysis of illumination beam angle
1 What is beam angle (beam angle)?
According to the definition of JGJ/T 119-2008, the beam angle is the angle between the two vector diameters of the luminous intensity curve expressed in polar coordinates on a given plane. The luminous intensity value of this vector diameter is usually equal to 10% or 50% of the maximum luminous intensity. As shown in the figure, when the peak light intensity is 50%, the included angle is 2x34°.
The beam angle is generally for luminaires, but it can also be used for reflective light sources, but it is not clear in this standard which case to use 10% and which case to use 50%.
In practical applications, CIE (International Commission on Illumination) recommends that the beam angle is 50% of the maximum light intensity; the IES (North American Society of Illumination Engineering) recommends that the beam angle is 10% of the maximum light intensity. For non-fully symmetrical luminaires, for example, in the cross-section of C=0° (and) at γ=0°, the angle of the beam with the light intensity of 10% of the peak intensity may be different, that is, the angle of the luminaire in the horizontal and vertical directions The beam angle may be different.
The beam angle of the lamp reflects the size of the spot and brightness on the illuminated wall. If the same light source is used in reflectors with different angles, the larger the beam angle, the smaller the central light intensity and the larger the spot. The principle is the same when applied to indirect lighting. The smaller the beam angle, the smaller the ambient light intensity and the worse the scattering effect. In addition, the beam angle of the lamp is also affected by the relative position of the light source and the lampshade.
In addition, when the angle contained in the direction where the luminous intensity is equal to 1/2 of the peak light intensity is defined as the beam angle, generally speaking, the beam angle of a narrow beam is less than 20°; the beam angle of a medium beam is 20° to 40°, and the beam angle is wide. The beam angle of the beam will be greater than 40°.
2 Application of beam angle
In practical applications, different beam angles have different applications. For example, a narrow beam is prone to produce high key illumination coefficients, and its strong light and dark contrast gives people a strong visual impact, which can catch people's eyes in the first time, but too high contrast will make the observer unable to see clearly. The details of the illuminated object, and the light spot is too small, will also cause the illuminated object to not be fully illuminated. For the K1, K2, K3, K4 lamps in the figure below, the beam angle is different, and the illumination effect on the screen is also significantly different. Of course, we also need to consider factors such as the distance, direction, and ambient brightness of the lamp in actual use.
The common beam angles are 10°, 24°, and 38°. Let's take a look at the schematic diagrams of the light distribution curves of the three beam angles:
We can see that the 10°angle lamp cup has a small illumination range, while the center light intensity is the largest, which can form a strong contrast on the illuminated surface; the 38°angle lamp cup has a large illumination range, but the center light intensity is the smallest, which is on the illuminated surface. The resulting spot is softer; the 24° angle effect is between 10° and 38°.
That is to say, for the lamp cup with the same power, the larger the beam angle, the smaller the central light intensity, and the softer the light spot. On the contrary, the smaller the beam angle, the greater the central light intensity, and the harder the light spot will be.
In practical applications, different beam angles have their own uses. In the picture above, 3 different beam angles produce 3 different effects on the statue.
The 10° angle gives people a strong visual impact with its strong light and dark contrast, which can catch people's eyes for the first time, but we found that: under the strong light and dark contrast, we cannot see the details of the plaster statue clearly. , And because the beam angle is too small, the statue is not fully illuminated.
A beam angle of 24° is much better than a 10° beam angle. The texture of the plaster and the appearance of the statue can be well displayed, and it also has a good visual impact.
The 38° lighting statue produces a soft and delicate effect, making it easier to observe the details of the statue. However, because the beam angle is too large, the background and the statue are mixed together, which makes it difficult to attract people's attention.
This is a comparison of different beam angles at the same power and at the same projection position. In actual applications, we have to comprehensively consider the projection distance, direction, environmental brightness and other parameters, and choose different lamp cups according to the needs.
If the surrounding environment has a high illuminance, a beam angle of 10° may be required, because the surrounding ambient light can make up for the area that it does not irradiate on the statue, and the beam angle of 10° creates a strong contrast on the statue. Good visual impact.
If the installation distance is relatively short, 38° should be selected. As the distance becomes shorter, the illumination range will also become smaller and the illuminance will also increase. Similarly, if the projection distance becomes longer, a beam angle of 10° should be selected.
