Energy conservation in buildings is greatly influenced by natural daylight in tropical region. A vital step towards development and promotion of daylighting technology in buildings is a prior study on estimation of exterior daylight availability for illuminating its interiors. In view of this, the present communication depicts the preliminary work progress carried out to arrive at a comprehensive idea on assessment of daylight availability and its characteristics. The study is reported taking the representative case of Bangalore (India) (latitude 12.97° N, longitude 77.56° E),which in future work facilitates to device suitable interior illuminance models and lighting controls for a daylight-artificial light integrated scheme. The objective of this paper is to document the estimation of spatial exterior daylight parameters like exterior horizontal as well as vertical global and diffuse daylight illuminance in addition to their respective luminous efficacies computed using an established analytical model. The paper also highlights user friendly computer simulation tool developed, for the detailed estimation of daylight availability at a particular region by the inclusion of corresponding solar radiation data.