How to choose the right goniophotometer according to the standard LM-79 and EN13032-1？

There is a wide range of goniophotometers on sale in the market, including central rotation type, rotation mirror type, double mirror type and so on. How to choose the corresponding goniophotometers for the tested lamps becomes the most important problem for the users. This article makes a brief introduction to this knowledge based on LM-79 and EN 13032-1.

A-α B-β and C-γ Co-ordinate System

According to EN13032-1, no matter what kind of goniophotometers is used, the main measurement plane must be based on the picture below when measuring the light distribution performane of the luminaire

1.    First axis
2.    Second axis
3.    Third axis
4.    Photometric Center

On this basis, the main coordinate systems used in the past are the following three:
1.    A-α：This coordinate system has not been used any more when testing conventional lamps and is only used to measure special lamps such as traffic, channel lights and indicator lights. Do not introduce it here. (Lisun LSG-1950 Goniophotometer for automotive and traffic signal lamps is specially designed according to this coordinate system)
2.    B-β：It is still used, but mainly for testing flood lights.
3.    C-γ：At present, it is recommended by the international standard which can guarantee the accuracy of the test at utmost.

B-β coordinate system
The schematic diagram is as follows：

1.    First axis
2.    Pole axis
3.    Third axis
4.    B Panel

• The first axis of the luminaire passes through the photometric center and is perpendicular to the B plane, which is also the main light emitting surface of the luminaire. The luminaire is measured by a photometric probe when revolving around the third axis and the polar axis.
• For non flood light, if you use the B-β test, the reference axis of the lamp need be taken as the third axis above, while the main light emitting surface is facing the probe, which means the probe is located on the first axis.

C-γ coordinate system
The schematic diagram is as follows：

1.    First axis (Pole axis)
2.    Second axis
3.    Third axis
4.    C panel

• The polar axis rotates on the C plane, while the C plane rotates around the polar axis. The photometric probe is located on the third axis
• When the lamp is still, the light emitting surface of the luminaire must be facing the probe, i.e., both of them are located on the third axis. If they are inconsistent and inclined, it need to be explained.
• The test results of C and B coordinate system can be calculated and swap. Lisun’s LSG-1890B/LSG-6000 provides two special test fixtures and can also direct conversion in software.

Goniophotometers Detailed Characteristics

The Goniophotometer is based on these two coordinate systems to carry the test, especially the use of C- gamma coordinate system products occupy most of the market. Based on this coordinate system, a variety of Goniophotometer with different working principles are derived.

1. Goniophotometer with Moving Mirror and Moving detector

LSG-6000 Moving Detector Goniophotometer fully meets LM-79 Clause 9.3.1 request. The tested lamp will keep burning position and be fixed. Near field detector, the lamp and the mirror are in the same line. During the test, the near field detector and the mirror will circle around the lamp, and the far field detector will rotate synchronously with the mirror.

• The instrument needs to be used in the darkroom, and the darkroom is equipped with diaphragms and light traps to reduce stray light and ensure the accuracy of the test
• According to the LM-79 standard, the color distribution test should be carried out while the photometric test is carried out. The user can select the color detector at the time of purchase, and test the color directly.

2. Central Rotation Goniophotometer (horizontal)

LSG-1890B high precision ratation luminaire goniophotometer system carries out measuring methods of fixed location and rotating luminaires. The measured luminaire is installed on the rotating supported, the center of which is in line with the rotating supporter center. The fixed photometry detector is testing the luminous intensity in various horizontal directions, while the light source rotating. The mechanical equipment allows turning the tested luminaires around a vertical axis and a horizontal axis. When tested luminaires turn around horizontal axis, the detector which is at the same level with rotating table will measure the intensity of each direction at this surface. When rotating with vertical axis, the detector will measure the intensity at the vertical surface.

This goniophotometer system has fast test speed, low requirement of darkroom, simple installation and maintenance, and high test accuracy for LED lamp. But for parts of the gas discharge lamp (such as fluorescent lamps, halogen lamps, etc.) because the lamp cannot be fixed in the lamp position, the accuracy will be lower than the two goniophotometer above. It is usually used to carry the factory inspection.

• Meets the test requirements of C-γof LM-79 and EN13032-1 standards and has higher accuracy for LED lamp.
• Needs to be used in the darkroom, and the darkroom is equipped with diaphragms and light traps to reduce stray light and ensure the accuracy of the test
• According to the LM-79 standard, the color distribution test should be carried out while the photometric test is carried out. The user can select the color detector at the time of purchase, and test the color directly.

3. Goniophotometer with color detector

There are two different ways to test the colorimetric parameters according to the descriptions of LM-79 part 12:
1.    Get the average value of the colorimetric parameters of the sample in space directly via measuring by an integrating sphere spectroradiometer system.
2.    Get the colorimetric parameters of each angle in space via adding a color detector to the goniophotometer system in the darkroom. We call the whole system “Goniospectroradiometer”. When second measuring methods are used, the interval and range of the detector scan should be consistent with the photometric measurements. The specific parameters can be seen in LM-79 9.3.3.

LSG-6000CCD moving detector goniospectroradiometer. The color detector is together with the near field photo detector.

LSG-1890BCCD high precision rotation luminaire goniospectroradiometer. The color detector is in the dark room.

• The principle of these type goniophotometers is adding a color detector and a spectroradiometer in the darkroom to the coaxial axis of the photometric detector to carry the test.
• If the color detector of LSG-5000CCD is installed in the near field, it can carry the test directly.

Conclusions

From the above, we can conclude that when selecting the goniophotometer, the following principles need to be followed:
1.    In addition to automobile lights and traffic lights, try to choose the C-γ coordinate system goniophotometer. ( LSG-1890B/LSG-6000 can carry the test of C-γ and B-β )
2.    To get higher test accuracy, try to choose the rotation mirror and rotation detector goniophotometer or rotation mirror goniophotometer. (LSG-6000, in the case of insufficient budget and testing the LED luminaire, horizontal goniophotometer can also be selected)
3.    The length of the darkroom (length of light path) shall be guaranteed at least 6 times longer than the longest axis of the luminaire to be measured.
4.    If need to test the spatial color distribution, the darkroom should be equipped with a special spectroradiometer and a corresponding color detector. (LSG-1890BCCD/LSG-6000CCD meets all requirements)

At present,there are other types of goniophotometer on the market such as double rotation mirror goniophotometer. Although it can shorten the length of the darkroom, but the mirror can’t reflect the light by 100%. Adding one mirror also can increase the test error and the angle between the mirrors should be strictly controlled, otherwise easy to affect the final test results.There are some near field rotation detector goniophotometers. Because of the limit of distance, they cannot test larger size of lamp. At the same time because there is no light trap and light bar, once the darkroom is broken, it could have an impact on the test results. There also is a limit of occasion.

Lisun develops the LSG-1890B/LSG-1890BCCD horizontal goniophotometer, LSG-6000/LSG-6000CCD rotation mirror & rotation detector goniophotometer according to years experience of research and development in the field of optical detection equipment, according to the different needs of customers, according to different application environments. Win the favor of large numbers of customers in the domestic and foreign markets. While providing the best cost-effective products, Lisun also ensure a high test accuracy and timely after-sales service.

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