A system for measuring a sample comprising: an integrating sphere light collector (12) for collecting light and containing the sample; a light source (24) for introducing light in the integrating sphere light collector (12), wherein the light source (24) is operable to output light with a known modulation, preferably by using a signal generator (26); a detector (22) for detecting scattered light in the integrating sphere light collector (12) and generating a signal indicative of the scattered light, and a lock-in amplifier (28) operable use the known light modulation and the signal generated by the detector (22) to provide an output for analysis.