Light is the major synchronizer of circadian rhythms to the 24-hour solar day. Compared to the visual system, the circadian system requires more light to be activated and is more sensitive to short-wavelength light. Without access to daylight, or electric lighting providing a comparable amount, spectrum, distribution, duration, and timing, human health and well-being may be compromised. This may be particularly true for those confined indoors, such as patients in hospitals and residents in care facilities. Architectural and design features, including window size, surface reflectances, and furniture placement, impact circadian stimulus levels. This paper details results of simulations used to determine the percentage of days that patients would receive a minimum level of circadian stimulation as a function of different window-to-façade ratios, surface reflectances, and latitudes.

The main aim of this article is to analyze the precision of several lighting simulation programs regularly used in daylighting studies for architecture, following the methodology established in the CIE test cases document. The 3DS Max Design 2014, Daylight Visualizer 2.6, DaySim 3.1b, Design Builder 3.0, Dialux 4.8, Ecotect Analysis 2011, Lightscape 3.2 and Relux Pro programs are analyzed. In order to establish the precision for each program, the sky component is measured at different points of study on the floor of a room, taking variable sizes and positions of openings into consideration. The results are contrasted with the analytical calculation of the sky component using Tregenza algorithms and the test cases established by the CIE, considering the models for Traditional and Standard Overcast Sky. Following the analysis of the sky component using the CIE test cases, it is concluded that the 3DS Max Design 2014 and Daylight Visualizer 2.6 programs present a maximum relative difference from the analytical model of close to 10%, while the DaySim 3.1b, Dialux 4.8 and Lightscape 3.2 programs show a margin of relative error lower than 30% in all case studies. Design Builder 3.0, Ecotect Analysis 2011 and Relux Pro show inadequate results.

The aim of this article was to assess some of the main lighting software programs habitually used in architecture, subjecting them to a series of trials and analyzing the light distribution obtained in situations with different orientations, dates and geometry. The analysis examines Lightscape 3.2, Desktop Radiance 2.0, Lumen Micro 7.5, Ecotect 5.5 and Dialux 4.4.