Ethylene Tetra Fluoro Ethylene (ETFE) foil is a useful alternative to conventional glass in architectural applications due to its consistent light transmission of above 90%. Demand for ETFE structures in tropical climates is increasing rapidly, in particular semi-outdoor ETFE structures are becoming noticeable in Singapore. However, building occupants are more likely to experience high levels of glare under the mostly sunny conditions in Singapore; inappropriate daylight control at transitional spaces between the interior and exterior could result in visual discomfort or an uninteresting luminous environment. Luminous assessments of clear ETFE structures in the UK and Europe are well-researched and documented. However there is a research gap in the manipulation of ETFE cushion’s transparency and opacity for achieving distinctive luminous environment and at the same time to deal with the consistent high solar radiation in Singapore. This paper aims to fill this gap through both qualitative and quantitative analytical studies. Semi-outdoor ETFE structures in Singapore are selected as a research vehicle. On-site luminance mappings of the ETFE structures were undertaken at different time of the year under sunny and overcast sky conditions. The luminance ratios obtained from the field work were used to identify the visual characteristics and brightness contrast on the selected visual fields. Theoretical parametric studies were performed to explore the luminous environments under the ETFE cushion with different foil densities and transparency by using digital models. Luminance ratios obtained from the on-site monitoring and that derived from the theoretical studies were compared and analysed to investigate the effects of ETFE cushion’s impacts on the internal luminous environment. The research results indicated that three main factors should be considered when designing a semi-outdoor ETFE structures: non-homogenous fritted patterns; appropriate manipulation of foil’s density; and light source direction control, which collectively contribute to a visually interesting luminous environment and enhanced visual comfort.