What are the types of goniophotometer

There are several common goniophotometers for light distribution. The difference between them lies in the geometric shape of the measurement, that is, how to collect photometric data and how to mechanically realize the measurement.

The types of Goniophotometers can be basically divided into Type A, Type B and Type C. For a detailed description, please refer to the 1987 edition of CIE 70. The difference between them lies in the way the lighting equipment rotates during the measurement and the photometric data obtained during this measurement. Several common goniophotometer test systems for light source distribution, the schematic diagrams of different types are as follows:

Type A

Type B

Type C

For photometric measurement of common products used for general lighting purposes, it is recommended to use a Type C goniophotometer. Type B or A is often used to measure road transportation and aviation automotive lights, projectors and model lights.

In practical applications, Type C Goniophotometer also have different designs. When measuring gas discharge lamps, the position during the measurement must be the same as the working position of the lamp under test, because changes in the position of the light source will significantly change the level of light output-lumens (total luminous flux), so the luminosity with a movable measuring arm is used Meter or Goniophotometer with reflective mirror. These two types of Goniophotometers are relatively expensive and require a larger darkroom to ensure an appropriate minimum photometric distance.

When measuring LED lights and general lighting products, the most commonly used is the Goniophotometer that rotates the light under test, and the measuring device is located at a fixed position far enough away, and the working position of the light-emitting diode will not fundamentally affect its performance and efficiency. The only difference lies in the way the heat sink dissipates heat, which may result in a decrease in light output. However, the difference in the total luminous flux output of the lighting equipment depends on the location of the lighting equipment, usually only exceeds 1%~3%, and can be corrected by using appropriate measurement procedures and the measurement results according to the internationally recognized standard CIE S025 E:2015 to make compensation.

LM-79 Moving Detector Goniophotometer (Mirror Type C) 

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