In paragraph 3.1. of Annex 4, Part 1 the position of the photometer head, the reference axis and the directions are clearly described. If the surface reflection is on the opposite side of the source from the photometer head, which is given at an angle of (β1 = -5°), the surface reflection has no influence on the measurement. This is true for the measurement of RI values as well as for colour measurement.
The proposed solution is based on an existing description in UN Regulation No. 27 (namely paragraph 2.6. of Annex 6) concerning the procedure to follow in case of a surface reflection for both colour measurement and CIL measurement.