This project is a major renovation to the existing building envelope (new skin added, new windows) and to the common area part of a tenant occupied office building. We have received approval from the USGBC to use LEED for New Construction. The core space lighting (elevator areas, lobby, restrooms, conference rooms), ductwork and finishes will be modified but the central air handling system and air cooled chiller and the tenant spaces will be only minimally altered. The question has been posed by the building manager regarding if they need to replace the tenant lighting in the space as the tenant space is not in the scope of work for the project. According to the ASHRAE 90.1-2004 users guide, if you were to replace more than 50% of the lighting fixtures in the building, you would have to meet ASHRAE 90.1-2004 lighting requirements, which, based on our analysis of what the base case and current design is in terms of lighting power density for this office building, means the building managers would have to replace all the tenant lighting with T8, 25 Watt lamps. However, if we replace less than 50% of the lighting in the building, we are not dictated by ASHRAE 90.1-2004, unless the renovation increases installed lighting power. However, according to the LEED Reference Guide for the prerequisite EAp2, lighting applies to all lighting installed on the building site including interior and exterior lighting. If the total installed interior lighting power is lower than the interior lighting power allowance calculated using ASHRAE 90.1-2004, the project complies. These two statements contradict each other if there is less than 50% of the lighting replaced, but the LEED Reference Guide does refer to the ASHRAE 90.1 users manual as a reference. Please advise on what to assume for the tenant space lighting power density in both the base case ASHRAE 90.1-2004 compliant building and the design case if less than 50% of the lighting is replaced.