The present paper presents a practical methodology to estimate the round skylight efficiency and hence the amount of daylight that reaches the interior of a room equipped with these devices. The methodology is based on flux transfer approach to model the distribution of the luminous energy inside the round skylights for various height-to-width ratios, wall reflectances and transmittances of the glazed cover under diffuse skylight and sunlight. (C) 2000 Elsevier Science S.A. All rights reserved.