The project is a four-story, 60,000 SF, speculative office building that is being submitted under LEED-CS. As we understand the intent, Credit SS8 - Light Pollution Reduction, aims to reduce light pollution through the control of interior lighting, exterior light distribution, and exterior lighting power density. Our question concerns the calculation requirements for the exterior lighting power density. We have been very diligent about reducing the overall lighting power density across the site. The site lighting has a 47% reduction of light power density as compared with the allowable light power density in ASHRAE 90.1.2004. All of our exterior site lighting is on a photocell/master time control system that turns off all non-emergency lights at 10pm. Because of the neighboring uses, we have voluntarily eliminated all building façade lighting on the western façade, which accounts for nearly a third of the total building façade. This allows us to focus our façade lighting on the public face of the building, adjacent to walkways, parking, etc.. Based on our total façade area (including the western façade) our lighting power density meets the credit requirement of 0.1 watts/SF. ASHRAE, however, calculates the LPD for each illuminated façade. Using this methodology, our LPD is 0.16 watts/SF, which is a 20% reduction from the ASHRAE standard. Does this meet the intent of the credit?
The CIR is inquiring if projects can combine the lighting power densities for all building façade lighting when calculating compliance for this credit. Per the referenced ASHRAE Standard, building façades must be calculated individually and are considered non-tradable (cannot be traded between surfaces or with other exterior lighting areas.) In order to demonstrate compliance with the requirements of this credit, projects must document a minimum 50% LPD reduction from the ASHRAE Standard Allowable LPD for building façade and landscape lighting for each individual illuminated façade. Additionally, the intent of the credit is to minimize the amount and overall intensity of installed site lighting to increase night sky access. Increasing the lighting intensity on one façade above the minimum requirements, although other facades are non-illuminated does not meet the intent of this credit. Applicable Internationally.