Through the influence on circadian rhythms, natural and artificial lighting, as well as lifestyle and architecture, affect health and performance. Epidemiological and interventional studies of light-initiated circadian biological outcomes require robust 24-hour data on personal light exposures, including blue light weighted irradiance data. The performance of the detection systems used is a key factor. We assessed the performance of 16 Actiwatch Spectrum™ devices for spectral response, directional response and dynamic range and propose techniques for calibration, deployment and data analysis for use of the watches in circadian studies. The results are presented, followed by a discussion of applicability focussing on spectral response for circadian studies.