Fenestration performance in nonresidentialsbuildings in hot climates is often a large coolingsload liability. Proper fenestration design andsthe use of daylight-responsive dimming controls onselectric lights can, in addition to drasticallysreducing lighting energy, lower cooling loads,speak electrical demand, operating costs, chillerssizes, and first costs. Using the building energyssimulation programs DOE-2.1B and DOE-2.1C , wesfirst discuss lighting energy savings from daylighting.sThe effects of fenestration parametersson cooling loads, total energy use, peak demand,schiller sizes, and initial and operating costs aresalso discussed. The impact of daylighting, asscompared to electric lighting, on cooling requirementssis discussed as a function of glazingscharacteristics, location, and shading systems.