Abstract:This paper examined the performance of a light shelf (LS) as a delighting device for reducing electric light usage in a south-oriented open-plan office (OPO) under the sky in the tropic using Integrated Environmental Solution Virtual Environment (IES VE). Results showed that the LS improved daylight quantity of the one-sided light office by reducing the excessive illumination at the area close to the window opening but increased it at the back where the illuminance is low. The improvement at the rear was from 1.55 % (LS 3 at noon on 21st March) to 2.99 % (LS 2 on 22nd June at noon). The LS also improved illuminance uniformity for visual comfort in the room with the best three test cases ranging from 74.07 % (LS 2 and 7) to 76.67 % (L3) compared to the case without LS. The selected test cases showed higher illuminance distribution between adjacent points or possible sitting position in the room than the base case (BC). The reduction in electric light usage ranged from 11.78 % (LS 3) to 15.97 % (LS 2). Hence, the paper concludes that LS improved daylight and electric energy efficiency. Therefore, the LS 2 is recommended for the south-oriented OPO with one-sided lighting in the tropical climate.