Providing natural light in residential spaces is a fundamental component of environmental quality, visual comfort, energy efficiency, and the health of occupants. In Part 4 of the National Building Regulations, light wells (light shafts) are defined primarily based on geometric minima—such as area and width—whereas their actual performance depends on orientation, floor level, and the angle of solar incidence. This study evaluates the performance of a 3×4 meter light well in the climate of Karaj, utilizing the "solar protractor" method. The central research question is: how much direct solar radiation does a 3×4 meter light well—designed in compliance with Part 4 of the regulations—receive across different orientations and floor levels in Karaj, and does the existing geometric criterion effectively guarantee adequate daylighting? The research employs an applied, descriptive-analytical methodology with a quantitative, performance-based approach. The primary tools used are the solar protractor and the sun-path diagram specific to the latitude of Karaj, which were used to calculate the annual hours of direct solar radiation for the light well across various orientations and floor levels. The findings indicate that the highest performance occurs on the third floor with a southern orientation, yielding 2,615 hours of annual direct radiation; conversely, this figure drops to 1,048 hours for an eastern orientation and to just 95 hours on the first floor. For southeastern and southwestern orientations, performance is also highly dependent on both orientation and floor level. These results highlight the necessity of shifting from a purely geometric,