Daylighting in urban streets in the tropics is affected by obstructions in the real street conditions. This paper proposes a method of estimating daylight in urban streets under overcast, partly cloudy and clear sky conditions. The concept of the daylight factor forms the basis of this paper with some assumptions to simplify the method. The calculated values proposed method were compared with the measured values from the survey in Bangkok. The results of the comparisons showed a high level of similarity. The calculation of the daylight factor or the absolute illuminance in streets could thus be obtained from the method described in this paper.