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Parking lot lighting based upon predictions of scene brightness and personal safety

Providing subjective impressions of security is central to outdoor lighting design. Current parking lot lighting recommendations are based upon photopic illuminances, regardless of spectrum. Scene brightness perception is directly related to impressions of security, and depends upon both light level and spectrum. A provisional model was used to predict scene brightness for three parking lots, each illuminated to different levels by different light sources. Observers judged scene brightness, security and other factors for each lot. The provisional model accurately predicted both scene brightness and security judgements. The lighting associated with the best subjective ratings also had the lowest power density. A design method using ‘brightness illuminance’ is presented, which can lower system costs while maintaining a sense of security by users.