The common goniophotometers with the mirrors can be classified into the following three types: The first one is the goniophotometer with rotating-mirror. A photo-detector is fixed in this goniophotometer. The luminous intensity of the luminaire under test in different directions can be detected through the autorotation of the mirror and the circumferential moving and autorotation in the space of the luminaire under test. As the luminaire under test is moving during the detecting process and the luminaire under test is in different environments with different positions, it is easily to be influenced by the environmental temperature and the air motion.
The second one is the goniophotometer with moving-mirror. The photo-detector is fixed or rotated with the moving mirror. With the mirror rotating around the luminaire under test and the autorotation of the luminaire under test in a fixed space position, the optical parameters of the luminaire under test in different directions can be detected. The advantage is that the luminaire under test has a fixed space position. Therefore, it cannot be easily influenced by the environmental temperature and the air motion; the disadvantages are that: the detected beam is changed with the cone and the detected distance is fixed. The large luminaire under test needs a larger space. In addition, since the detector is fixed and cannot follow the rotation, the sensitivity difference of the detector in different directions of the space can lead to a relatively big error.
The third one is the goniophotometer combining the moving mirror and the fixed mirror. The moving mirror and the light detector are fixed on the same rotating arm for synchronously rotating around the luminaire under test. In addition, a fixed mirror is arranged outside the detecting table for coordinating the moving mirror and the photo-detector. The advantage is that: the luminaire under test has a fixed space position, which is not easily to be influenced by the environmental temperature and the air motion; the disadvantage is that: the detected beam is always changing while rotating around the cone. Since the detector and the moving mirror are moving synchronously, it is difficult to arrange a series of diaphragms for eliminating the stray light between the detector and the light source. Or else, light beam blind angle can be existed; the beam axle is entered to the fixed mirror through each direction of the conical surface, and then reflected to the moving detector. Since the reflectance of the mirror in each direction of the space are discord, the obvious luminous intensity error will be introduced; besides, the surface shape error of the fixed mirror will cause that the detecting accuracy of the luminous intensity is sensitively influenced by the surrounding reflected stray light.