This study attempts to verify the accuracy of energy savings prediction using a daylight responsive dimming system. To accomplish this, the real-time power consumption of electrical lighting in a mock-up space was compared with the power consumption that was calculated using 'the prediction method' (Method A), which was suggested to improve the accuracy of the predicted amount of energy savings. In addition, this study suggested the 'indirect illuminance' concept (Method B) to improve the system performance and predict the lighting energy savings potential of a system because certain inherent problems that are caused by the open-loop proportional control algorithm used were identified. Regarding the accuracy of the prediction method, 'Method A' considers the non-linear dimming curve of the luminaires and thus generated data that were more similar to the real measured lighting power consumptions. 'Method B' generated higher energy savings potential (e.g., 36.9-73.8%) compared with those of Method A (e.g., 27.6-72.9%) on each day. (C) 2016 Elsevier B.V. All rights reserved.