Do you think you really understand the beam angle?

Figure 1:

Figure II:

What is the difference between these two figures? In fact, two different expressions of an IES light distribution curve. Figure 1 is a rectangular coordinate representation, and Figure 2 is a polar representation. It is one of the methods to represent the light distribution curve, and it can clearly find the data of the core requirements in the figure.

We learn the IES light distribution curve knowledge. The first thing to learn is the beam angle. What is the beam angle?

A simple definition:

Definition of CIE International Lighting Commission and China National Standard GB: On the plane of the beam axis, the center point of the front of the lamp is the axis, the angle of the peak center intensity is 50%, the English name Beam Angle, unit: ° (degrees) .

Different from CIE is the definition of IES of the North American International Illumination Society: the angle between the peak center intensity of 10%, the English name Filed Angle.

Since our national standard lighting is based on the CIE International Lighting Commission standard, we generally say that the angle of the lamp is the angle of the 50% light intensity of the Beam angle, so whether it is an optical manufacturer, the lighting manufacturer or the designer can unify first. Let's take a look at this concept.

In China and most countries, the beam angle is the angle between the 50% peak center intensity, not the filed angle at 10% peak intensity, to avoid misunderstandings and disputes. (Off topic: This is the question that I was "questioned" by the customer before the opening of the question. With the 25° lens of the Filed angle PK, the "brightness" of my Beam angle 23° lens, I am also drunk)

The Cartesian representation is shown below:

The above illustration has a total of 8 knowledge points:

Note 1:

Peak center light intensity: It can be seen from the figure that Imax=930cd, the intensity of the peak light determines the intensity and illuminance of the illumination (of course, the illuminance also considers another important factor: distance)

Note 2:

50% peak center light intensity: 1/2 Imax = 465cd, here mainly to see the beam angle angle.

Note 3:

Beam angle: that is equal to 50%. The full angle of the angle (not half angle) at the peak light intensity is added to the left and right = 64°. The size of the beam angle determines the size of the spot and is closely related to the effect.

Note 4:

The unit cd/klm in the lower left corner indicates that the above data is based on 1000lm data, that is, if your fixture is 5000lm output, the peak light intensity = 930*5000=46500cd. (cd/klm reflects the power of optical design and luminaire design).

Note 5:

C0-C180 represents the X-axis plane, and C90-C270 represents the Y-axis plane (obviously seen at the asymmetric beam angle).

Note 6:

Efficiency: Generally expressed as the efficiency of a luminaire or optics, the higher the better. (Efficiency reflects the utilization factor of light, which is the most important strength manifestation).

Note 7:

10% peak light intensity: 1/10 Imax=93cd, mainly to see the filed angle of Note 8.

Note 8:

Filed Angle: equal to 10% of the full angle between the peak intensity, this figure is about 90°.

The above are the 8 key points of the Cartesian IES file, and the polar coordinates are based on the polar coordinates.

Let's look at the spot area of ​​the spot under the beam angle (in fact, my understanding is that single-light effects such as museum lighting consider 10% peak light intensity angle is more important, if it is functional lighting or floodlighting, focus on 50% light intensity angle and light The smoothness of the pattern is closer to the cosine and the smoother it is).

Let's take a look at some of the IES light distribution curves and applications for typical lighting applications:

Office lighting:

Supermarket lighting / warehouse lighting:

Commercial lighting such as downlights:

Street lighting:

There is a problem when you come here. The same beam angle, is the effect of light the same? The answer is very negative. The beam angle only represents the illumination range of the light. It does not reflect the intensity of the light in each subdivided angle region. Give a chestnut:

Take a closer look. In fact, the above four figures are two IES light distribution curves (represented by Cartesian coordinates and polar coordinates). The angles are all large angles (the two angles are different, one is 132 degrees and the other is 161°). ) But the light distribution of the two is completely different.

The first is the light distribution curve of the gas station lamp, the purpose is to distribute the light evenly below the lamp;

The second is a similar light distribution of the lawn lamp, the purpose is to spread the light evenly to the surrounding area.

The requirement for light energy distribution from the US DLC is how much light energy (standard for rational use of light) is distributed over a specific range of angles to meet the different light requirements of each lamp.

Figure: The light distribution of the oil station lights is to evenly light the area

Figure: The light distribution of the lawn light is for the distribution of light around the four, rather than the front lighting needs.

I hope that the above sharing of IES light distribution knowledge can be useful to you, but always need to grasp: look at the real light distribution curve, find the core data, understand the light distribution of the lamps, use the light reasonably, reduce the light pollution, and save energy. Low carbon.