IECC 2009 contains a number of changes impacting lighting for commercial buildings, including:

• Forced choice of compliance with entirety of IECC or 90.1
• Required circuiting for independent control of lighting in “daylight zones”
• Revision of additional retail display allowances
• Added exemptions to interior lighting wattage that must be counted for compliance
• Splitting the exterior power allowance using a system of outdoor lighting zones
• Clarifications and practical application language changes

In terms of lighting, ASHRAE 90.1-2007 clarifies the Standard’s intent and enacts several refinements but otherwise doesn’t revise the lighting power density (W/sq.ft.) limits from the 2004 version, which itself was 20-25 percent more stringent than the 1991/2001 versions.