Methods for correction of the LIDC by means of goniophotometers with rotating luminaires for different lamps

Goniophotometry is the fundamental measurement method for the measurement of spatial distribution of the light output of luminaires. The measurement results are represented by luminous intensity distribution curves (LIDC). This information is used by lighting designers for computation of photometric parameters to predict photometric values in real lighting installations. Therefore accuracy of the measurement of the LIDC is very important to provide the best information for other processing. In practice for this type of measurements various types of goniophotometers can be used according to recommendation CIE 121:1996. The main purpose of the recommendation is to describe the different types if goniophotometers and to give recommendations to the measurement process. Currently this document is under revision to implement the new approaches in the field of goniophotometry. One of the most common type of instruments is the goniophotometer with rotating luminaire. Due to the simplicity of construction, moderate space requirements and favourable price most of the testing laboratories are using this type of goniophotometer for measuring LIDC of luminaires. There are possible errors present due to work position of luminaire in Earth gravitation field is changing by rotating the luminaire around its axis. The CIE recommendation tells if this type of goniophotometer is used correction should be applied e.g. by means of auxiliary photometer or other possible methods. The auxiliary photometer during the actual measurement can shade luminous parts of the luminaire what can influence the shape of the LIDC and also the derived photometric results. This paper deals with investigation of the correction methods in goniophotometric measurements using luminaire rotating goniophotometers. Results of measurements of LIDCs were validated by means of other type of goniophotometer which did keep the work position of the luminaires (mirror goniophotometer) during measurements. Conclusions of this work should provide recommendation for methods of corrections in goniophotometry of LIDC of luminaires which LIDCs are measured with luminaire rotating type of goniophotometer. Furthermore paper reveals the possible errors which can occur in the measurement of LIDC of luminaires with various types of lamps.