Energy Saving Potential of Lamps with Different Spectral Composition in Outdoor Lighting Applications under Mesopic Photometry System

Various streets and outdoor lighting applications are subjected to mesopic vision and mesopic photometry system. Although the lighting design for these applications are performed considering photopic region, it is appropriate to consider the mesopic effects for visually effective and energy efficient lighting design. The adaptation luminance and mesopic luminance should be considered along with the photopic luminance during the lighting design of these application areas. In this paper photopic luminance due to a light source is computed from it's luminous intensity distribution table. Corresponding mesopic and adaptation luminance values are also computed in presence of two different surrounding lighting conditions with different spectral compositions. All those parameters are measured again in laboratory environment for same lamp combinations. From both the computed and measured data it has been found that the lamps with more blue content in its spectrum i.e. the lamps with higher scotopic/photopic (S/P) ratio provides higher mesopic and adaptation luminance as compared to the corresponding photopic luminance. A sample road stretch is designed and the unit power density (UPD) values are computed for all the lamps. As these cool white lamps are more effective in mesopic vision, hence number of lamps required during the lighting design is less which leads to less power and less energy consumption for any particular application area.