Abstract
The indoor visual comfort of subjects faced with indoor ambient lighting varies with the position of the subject and is not constant over time. Average performance indexes, such as the mean value of Daylight Factor and Daylight Autonomy, are commonly used to analyse lighting distribution. These indexes, however, don’t properly take into account either the spatial or the time distribution of values affecting the non-uniformity of environmental lighting. Indeed, these are limited to the definition of a mean value or to the assessment of time availability of daylighting. This paper examines spatial and temporal non-uniformities in indoor lighting as possible causes of discomfort for occupants. The goal is to propose and verify possible supplementary tools to integrate traditional methods of evaluating ambient indoor lighting. Use of the entropy theory with a probabilistic approach can help to obtain more detailed information about the environment. The authors have developed a case study of several sample environments and have analysed the relationships between lighting parameters and typical indices of information theory. Results show that this approach could be a useful way for predicting possible indoor visual comfort issues and for developing a preliminary assessment to a sustainable building design.
Highlights
A proper lighting design that will ensure comfort for visual tasks must focus on the appropriate ambient lighting distribution
In the investigated spaces good correlations have been found between the DFavg and the entropy ratio H/Hmax calculated for the values of illuminances at several points on workstations
In the analysis of spatial distribution, the better correlations are associated with data series for specific visual task areas
Summary
A proper lighting design that will ensure comfort for visual tasks must focus on the appropriate ambient lighting distribution. CBDM predicts various radiant or luminous conditions using sun and sky data derived from standard meteorological datasets [6,7,8] These analysis methods give information about the daylight availability, but do not give any information about the illuminance distribution values [9]. If the lack of lighting uniformity in a room is considered a weakness, the quality of the space can be investigated through this type of analysis By this approach, the internal environment is analysed as the signal source, while the subject is the receiver. It is necessary to underline that in order to calculate H and Hmax for a given series of values it is necessary to set the number of intervals of illuminance in order to account for the probability pi of occurrences within the intervals. H/Hmax-t has been reported for each time series in all considered latitude calculations
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