Daylight and planning in Europe

This work addresses issues related to daylight in urban canyons in predominantly sunny climates. Reflected sunlight from obstructions and ground is a major contribution to the illumination of buildings in orientations and at times when the sun is behind the building. Physical measurements collected in an urban canyon in Lisbon showed a linear relationship between the global horizontal illuminance and the total vertical illuminance when the facade is not receiving direct sunlight. Further studies carried out with computer simulations with RADIANCE as well as analytical calculations confirmed this relationship, which is shown to be relatively stable throughout the year, with latitude and orientations and time of day when sunlight is reflected off obstructions and ground. Moreover, the slope of this linear relationship is relatively similar for different floor heights and canyon ratios. Thus, the equation is representative of the whole year condition and fairly robust for individual parameters. It may therefore be used for quick calculations in the initial design stages of the project. Daylight calculations are commonly based on the daylight factor method regardless of prevailing weather conditions. While this method may be used for overcast sky conditions, it can be argued that it is not appropriate for clear skies. A relationship emerged which forms the basis for the average total daylight factor calculation in an urban canyon, taking into consideration reflected sunlight. In a similar way to the average daylight factor it may be used as an indicator of how well lit the indoor environment is and allows for the sizing of windows under predominantly sunny climates. All the above gave the basis to the definition of guidelines for daylight and urban planning in Europe. Two different set of criteria are presented. They apply to predominantly overcast and clear sky conditions. Both, individually or combined, allow for daylight design in European climates