VCP and UGR Glare Evaluation Systems: A Look Back and a Way Forward

Abstract

We review the discomfort glare evaluation systems of the Illuminating Engineering Society of North America (IESNA), Visual Comfort Probability (VCP), and that of the International Commission on Illumination (CIE), Unified Glare Rating (UGR), as they apply to interior electric lighting. We provide an overview of the history and research behind them and an extensive bibliography.The current IESNA Handbook states that the VCP is very limited in applicability to modern lighting systems, and was validated for lensed fluorescent systems only. The CIE's UGR system has been shown to be a good predictor of human responses for lensed fluorescent systems. Recently, the CIE has proposed extensions to the UGR discomfort glare model, which are applicable to most modern lighting systems, including small, large, and complex systems. We provide a review of these extensions and the research behind them. There are many similarities between VCP and UGR and only minor differences, and so we recommend that research be undertaken to validate the UGR's extensions to small, large, and complex systems.