126 TECHNOLOGY / GLARE CONTROL CASE STUDY
headlights on a country road where the glare source is small and bright against a darker backdrop. These glare sources make it difficult see duller objects near the source.) Disability glare is caused by light scattered within the eye, often due to the entering of excess light. This scattering lays a luminous veil over the retinal image and reduces the contrasts within the image. Furthermore, the time taken to recover from disability glare effects extends with age (Theeuwes and Alferdinck - 1996). It is standard practice for Network Rail to issue drivers with sunglasses to aid their vision against discomfort glare. However, disability glare will prevent the train drivers doing their tasks safely and action would be required at Birmingham New Street Station to ’design out’ any sunlight reflections from the façade which may affect the train drivers ability to do their job.
MOCK UP Under clear sky conditions, significant sunlight images and reflections were recorded on the façade and the ground beneath the mock up. It was observed that
these reflections were dependant on the viewing location, degree of cloud cover and orientation of the façade panels. Under clear sky conditions, multiple images of the sun were experienced in a number of locations on the façade which were of high luminance and manifested into ripples of reflected sunlight on the ground beneath. These on site findings led to the need for a pioneering investigative study to be carried using Radiance software to simulate the impact of glare from indirect sunlight being reflected from the proposed façade.
SUNLIGHT SIMULATION As expected, a number of locations on the track bed were found to experience significant areas of reflected sunlight. These were analysed and the veiling luminance was found to exceed the 500cd/m2 threshold on a number of occasions during the driver’s approach to the station. The data was presented to the design team, architect and railway signalling specialists to determine any adverse effects which may be possible from the disability glare. With the assistance of the Architect the facade profile design was then optimised to deflect
the reflections away from those areas of track identified as exceeding the threshold or reduce the duration of the disability glare effects to a tolerable level.
FUTURE VISION This pioneering work has undoubtedly helped to fulfil the ambitions of its visionaries in providing a façade design that is both revolutionary in its architectural form and unique in its outward silvery metallic appearance. This has now been made possible with the knowledge that the reflected glare to train drivers and effects to track signals has been considered within the design of the architectural façade. The unique surface mirroring effect will undoubtedly help to make this state of the art building a future landmark within the City of Birmingham and to the wider world.
www.arup.com
Birmingham New Street Station Gateway Project Client: Network Rail - Azhar Quaiyoom Architect: AZPA - Charles Valla
Lighting Consultants: Arup - John Waite, Richard Morris, Giulio Antonutto
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