Reductions in lighting energy have secondary effects on cooling and heating energy consumption. In general, lighting energy reductions increase heating and decrease cooling requirements of a building. The net change in a building's annual energy requirements, however, is difficult to quantify and depends on the building characteristics, operating conditions, and climate. This paper characterizes the effects of lighting/HVAC interactions on the annual heating/cooling requirements of prototypical U.S. commercial buildings through computer simulations using the DOE-2.1E building energy analysis program. Twelve building types of two vintages and five climates are chosen to represent the U.S. commercial building stock. For each combination of building type, vintage, and climate, a prototypical building is simulated with varying lighting power densities, and the resultant changes in heating and cooling loads are recorded. These loads are used together with market information on the saturation of the different HVAC equipment in the commercial buildings to determine the changes in energy use and expenditures for heating and cooling. Results are presented by building type for the US as a whole. Therefore, the data presented in this paper can be utilized to assess the secondary effects of lighting-related federal policies with widespread impacts, like minimum efficiency standards. Generally, in warm climates the interactions will induce monetary savings and in cold climates the interactions will induce monetary penalties. For the commercial building stock in the U.S., a reduction in lighting energy that is well distributed geographically will induce neither significant savings nor significant penalties from associated changes in HVAC primary energy and energy expenditures.