Abstract The objective of this paper was to address the combined effect of using two solar screen parameters, together under the desert clear-sky. The paper examined the effect of the screen axial rotation and its opening proportion ratio on the year round daylight performance, and the resultant glare phenomena probability. A typical residential living room space was selected for assessment. Simulation was carried out using the climatic data of the city of Jeddah, Saudi Arabia, which enjoys a desert clear-sky. It was conducted using Diva-for-Rhino, a plug-in for Rhinoceros modelling software. It was used to interface Radiance and Daysim for annual simulation and illuminance computation. The combined effect was simulated in two phases. The first phase studied the impact of these solar screens parameters on year round performance using dynamic Climate Based Daylighting Metrics (CBDM). While the second one evaluated first phase results in regards to the probability of glare phenomena. For each of the four main orientations, four different designs were simulated and compared. It became apparent that solar screens can drastically improve the daylight distribution in rooms and spaces. “Daylit” areas occupied 60% to 72 % of the spaces when properly planned solar screens were employed. It reached 90% of the space in the typically problematic North orientation. Also, the glare phenomenon was eliminated in the East, West and South orientations. However, design of solar screens should address the specific particulars of each situation. Combining screen parameters can yield very promising results if planned and tested carefully. Keywords: Solar screen, Daylight Availability (DA), Daylight Glare Probability (DGP), Dynamic Climate Based Daylighting Metrics (CBDM), Sunny desert clear sky. 1 Introduction Provision of natural daylight in residential buildings is very important. It creates a dynamic and pleasant appearance, while reducing the energy consumption of artificial lighting. This is especially relevant in desert locations that are endowed with abundance of clear skies. However, uncontrolled daylighting could result in the incidence of uncomfortable glare and overheating of spaces due the admittance of direct solar radiation. This is especially relevant in the clear and bright sunny conditions of the desert skies. Movable lighting control systems, such as venetian blinds, are typically used for control of daylighting. They are typically fixed externally or internally to control light penetration through openings. However, several studies reported that the use of movable shading systems often result in reduced utilization of natural daylighting. Reinhart et al. (2011) reported that the behaviour of users varied, where a reasonable percentage of occupants never open the blinds or rarely do; even with more recent motorized blinds the issue of blocking the view to the outdoors still existed. Sutter (2006) found that remotely controlling the blinds can increase their movement three times more than manually controlled ones. However, users were found leaving the blinds lowered most of the time. External Perforated Solar Screen Parameters and Configurations: Daylighting Performance of Screen Axial Rotation and Opening Proportion in Residential Desert Buildings Hanan Sabry 1 , Ahmed Sherif 2 , Mahmoud Gad Elhak 1 & Tarek Rakha 2 1 Department of Architecture -Faculty of Engineering - Ain Shams University 2 The American University in Cairo