The main aim of this article is to analyze the performance of lightwell skylights under overcast sky conditions, determining the daylight factors and luminous distribution produced inside a room. Four different studies are carried out considering a room with a lightwell skylight. The first analyzes the daylight factors according to the size and height/width ratio of the skylight, the second evaluates illuminance depending on the reflection index of the lightwell, the third studies different room proportions and the fourth establishes suitable spacing between skylights. All tests were carried out using Lightscape 3.2 software. Following the trials, it was concluded that daylight factors are almost directly proportional to the size of the skylights and inversely proportional to their height. There is also an approximate quantification of the influence of the reflection index of the lightwell on interior lighting. Finally, it is confirmed that, in the absence of a reflected component, the suitable spacing between openings is proportional to the height/width ratio of the skylight. (C) 2013 Elsevier B.V. All rights reserved.