Daylight Concepts

Spatial Daylight Autonomy

Spatial Daylight Autonomy (sDA) examines whether space receives enough daylight during occupation hours (8 a.m. to 6 p.m.) on an annual basis using hourly illuminance grids on the horizontal work plane (700mmx700mm) on the height 760 mm. In lieu of collecting a year’s worth of data in the field (Typical Meteorological Year). It references a local climate file EnergyPlus Weather file available from a local meteorological station to run hourly illuminance maps.

Test point in the building model that achieve 300 lux for at least half of the analysis hours count as meeting the daylighting threshold. As a result, sDA values can range from zero to 100 per cent of the floor area in question. An sDA value of 75 per cent indicates a space in which daylighting is “preferred” by occupants; that is, occupants would be able to work comfortably there without the use of any electric lights, and find the daylight levels to be sufficient.

Annual Sunlight Exposure

ASE is intended to help designers limit excessive sunlight in a space ASE measures the presence of sunlight using annual hourly horizontal illuminance grids. ASE uses a simulated 1,000 lux as an indicator value for sunlight, direct sunlight.

ASE is rather an indicator of overlit than of a glare. ASE values range from zero to 100 per cent, with the latter suggesting that the entire floor area of the space in question exceeds the simulated value of 1,000 lux for at least 250 hours per year.

Daylight Glare Probability

DGP index considers vertical illuminance at the eye level, has been identified as one of the reliable metrics, since it was based on experiments with real human subjects. In this study, extensive experiments were conducted in a full-scale private office environment with dynamic shading controls, to measure interior luminance and illuminance conditions under variable sky conditions and shading control strategies. The west facade characterizes with significant glare, especially in the period from October to March when the sun is low on the hemisphere. Annual Sunlight Exposure measure how much light of more than 1000 lux reaches the test surface. To receive points in the LEED certification program maximum of 10% of the test surface can have more than 1000 lux. According to the LEED basics, even small excess could lead to a significant decrease in visual comfort.

LEED does not consider facades without the dynamic anti-glare system. For that reason, Daylight Glare Probability method is used to verify the solution. ASE is performed as a driver that decreases the amount of unwanted daylight. Daylight Glare Probability is a measuring method coined by Wienold and it takes into consideration human behaviour and office space flexibility. In the numerous work, Wienold proved that this method is more reliable and efficient. To check whether a user will be affected by the glare a fisheye render view is produced. The advantage of this method is that a designer can choose a different view than a view of the window. Also, the designer can pre-define a spatial distribution and claim a working space in the well-lit part.

Daylight Factor

The Daylight Factor (DF) is an easy way to measure the subjective daylight quality in a room. It describes the ratio of outside illuminance over inside illuminance, expressed in per cent. The higher the DF, the more natural light is available in the room.

DF does not consider location, the orientation of the building. It is a good method to quickly compare two geometries, but only if they are already meeting DA requirements. Several scientists claim that this method used by BREEAM and DGNB-Daylight Factor-is outdated.

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