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LIGHTING SPECIAL SCHOOLS


Daylight analysis results


The results can be either a single value to show the room satisfi es the daylight autonomy (DA) criteria or a graph that can be more informative and aid understanding of the benefi ts of the light redirecting systems and secondary glazing


A lightshelf is reducing the perimeter DA and distributing the light to the back of the classroom


76 70


58 64


The secondary glazing at the back of the classroom has increased the DA


At this point in the room the DA is approaching the target minimum of 50%


environment. This emphasis on daylight is well documented in the Hershone Mahone Group studies, among others. Of equal importance is that lighting is not included within the building services section. The FOS recognises the crucial relationships that exist when creating a lit environment. Designing for daylight is the priority, followed by an electric lighting solution. The electric lighting solution must both meet the needs of the occupants of the space and respond to the known distribution of daylight. Lighting control is introduced to ensure the systems operate effi ciently and in line with user requirements. Finally, the ongoing operation, measurement and maintenance is designed and recorded to ensure the lighting solution delivers what was promised. The fi rst stage in lighting the learning environment is to consider the daylight available. This is where we see the major change for the PSBP, compared with previous building programmes and associated school lighting guides and specifi cations. The FOS fi rst describes the desired outcome for the learning environment – for example, light from two sides of the room to create balance, well-lit soffi ts and walls to give the room brightness, and control of glare to ensure the result is not the familiar ‘blinds down, lights on’ scenario. The specifi cation then goes on to set numerical daylight parameters and, in place of daylight factors, climate-based daylight modelling (CBDM) has been adopted.


www.cibsejournal.com The phrase CBDM was fi rst coined


by John Mardaljevic in 2006 when he presented the concept to the CIBSE National Conference. Since then the principles have been discussed at many daylight and lighting events, as well as introduced into the text of BS 8206-2: 2008 Code of Practice for Daylighting and LG5: Lighting in Education (2011). The concept is quite simple: rather than simulate the quantity of light within a space through the use of an overcast sky model, CBDM makes use of actual weather data and, as a result, time-


Useful daylight index (UDI) UDI <100 [%] UDI 100-3000 [%] UDI >3000 [%] 86 81 79 77 76 80 89


Lighting design is the primary heading in the environmental requirements section, a refl ection of the value placed on daylight within the learning environment... Of equal importance is that lighting is not included within the building services section


52 46 40


76-80 70-76


58-64 64-70


52-58 46-52 40-46


89 85 76


16 3 1 2


The sample graph here shows the results of a UDI analysis for a classroom. Each line represents the results as if a line had been drawn down the centre of the room from the external window to the back wall. A 3D graph would provide further detail


20 1 3


22 1 4


Secondary glazing will improve the UDI 100-3000 as it reduces the UDI <100 fi gure


23 1 5


15 5


6


The target is a UDI 100-3000 of 80% for the learning space


11 3


7 10 1 8 9


8 3


9 6 10


UDI >3000 will always rise adjacent to external glazing, equally UDI <100 will always reduce


2


22


December 2012 CIBSE Journal 9


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