At present, goniophotometers we often use basically have two sets, goniophotometer with rotating mirror is one of them.
The detector of this kind of system is fixed on the position of 19.83 m; the constant temperature device added on the detector makes the temperature keep 35℃. This testing system has three rotation axes. The spindle drive reflector rotates around the center, which makes the light of the lamp reflect on the detector. At the same time, synchronous reverse rotation of the lamp arm adjustment shaft always keep the lamp holder in the upright position, so as to realize the measurement of the lamp in Y direction. The detector and the live spindle are in the same line. 。C-γ axis rotation actually is rotation of the vertical sphere rotation axis (horizontal axis) centered on the lamp by the detector, in order to realize the measurement of the lamp in γ direction. Its motion curve is equal to the direction of latitude line. The detector measures the light intensity of illuminance value of each meridian and parallel junctions. Lamp in this kind of structure can be measured in C plane or cone system. Beam axis is measure as unchangeable in the rotating reflector type distribution photometer. Diaphragm that can remove the stray light is installed between the photo detector head of the instrument and the measured lamps; the reflecting stray light emitted by the lamp on the ground surface or wall surface is effectively removed. In addition, electric aperture is installed on the first optical hole behind the reflector. When measuring the lamp with different kinds of size, we can adjust the optical aperture size according to the size of the lamp so as to effectively remove the stray light. Therefore, the stray light of the device with this kind of structure is rather low, but the accuracy is high.
In this set of equipment, the measured lamp should make circular motion in bigger space, the temperature exists much instability.
Lamps should make translational motion, air will change the temperature distribution around lamps, so international lighting committee made the regulation on the movement speed of the lamp with this kind of structure according to the research of the CIE experts that air velocity around the lamps should be less than 0.2 m/s, to meet this requirement, the movement speed of this lamp should be as slow as possible. Therefore it would take a relatively long time to achieve high measuring accuracy.
There always exist the phenomenon of upper high temperature and bottom low temperature in the dark room. The measured lamps are actually working in the alternating environment temperature. The temperature difference is usually 2℃～5℃, and the moving space is bigger, the temperature difference is bigger. Therefore, there will be bigger error on the test for the lamp or luminaires with very sensitive temperature.
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