During the growing season, both temperature and light intensity have major impact on plant growth and development. However, the probability of the incidence of high temperatures and/or heat events is likely to increase and become a significant phenomenon in Australian viticulture in the future because of potential climate change. During heat events, high temperature is likely to be exacerbated by the addition of high light intensity or radiant energy/heat which is already a characteristic feature in some Australian vineyards at present and it is expected to continue into the future. Despite its importance, there are few studies on the interactive effects of photon flux densities and temperature of the radiant load on grapevine physiology. This study quantified the impact of temperature and light on grape yield, sugar content and sugar accumulation. We have used Vitis vinifera 'Shiraz' in the field over two seasons under four different light intensities using shade cloth of variable densities. Yield was reduced by 22-40% under the lowest light intensity. Berry sugar content was reduced by 13% under the lowest light intensity in the cooler season (2012-13) and increased by 13% under the highest light intensity in vines exposed to a natural heat event (2013-14 season). Further, sugar accumulation rate declined by 7.7-11.4 mg berry-1 day-1 under the high light intensities. This study has showed that lowest light intensity was a cost for the yield and sugar content during cooler conditions. However, sugar content and sugar accumulation rate under the high light were lower in the warmer conditions.