NCEUB Conferences, 13th International Radiance Workshop 2014

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Solar reflected Glare
Luisa Brotas, Jan Wienold

Building: Arup 8 Fitzroy St.
Room: Emmerson & Shears Room
Date: 2014-09-03 01:30 PM – 02:00 PM
Last modified: 2014-08-24

Abstract


Visual comfort is important to the wellbeing of people and their productivity. Daylight is often acknowledged as contributing positively towards visual comfort. However, under certain conditions can be a negative effect and create discomfort or disability glare. Glare may occur when there is too much light, when the luminance range is too high and is within a given view angle of the observer. The wrong combination of these may have an impact on the ability of a person to perform a visual task.

This paper addresses the disability glare created by veiling glare and the effect it may have of reducing the visual performance in outdoor spaces. Veiling glare is a particular case when light is reflected off a surface and causes annoyance or impairment of a task to the person in a particular view angle. Two factors that determine the nature and magnitude of veiling reflections are the specularity of the surface being viewed and the geometrical relationship between the observer, the surface and any source of high luminance. (SLL 2009)

In outdoor tasks or overlooking windows with reflected solar dazzle ahead it is of major importance to assess the magnitude of disability glare as the impairment of vision can cause accidents. There are three dimensions to glare: temporal, spatial and intensity. For these it is important to predict the times of day and year when solar dazzle can occur. Because of its high intensity, one may assume that if solar refection is within the field of view it will cause glare. Therefore it may be sufficient to estimate the period and position when it may occur.  Littlefair (1987a and 1987b) provides the formulae to assess and quantify solar dazzle reflected from glazed facades. Computer simulation programs are also available. (Wienold, 2006).

This paper presents a case study where reflected glare is of particular concern.

References

CIE (1999) CIE Collection 1999: Vision and Colour: Physical Measurement of Light and Radiation, 135/1 Research note: Disability Glare, Commission Internationale de L'Éclairage, pp.1-10

CIE (2002) CIE Collection on Glare 2002: Equations for disability glare, 146 CIE TC 1-50 report and Glare from small, large and complex sources, 147 CIE TC 3-01 report Commission Internationale de L'Éclairage

Littlefair, P. (1987a) Prediction of Reflected Solar Dazzle from Sloping Facades, Building and Environment, 22(4), pp.285-291

Littlefair, P. (1987b) Solar dazzle reflected from sloping glazed facades, IP 3/87, Building Research Establishment, Garston

SLL (2009) The SLL Lighting Handbook, London: The Society of Light and Lighting

Vos, JJ. (2003a) On the cause of disability glare and its dependence on glare angle, age and ocular pigmentation. Clinical and Experimental Optometry 86(6), pp.363-370

Vos, JJ. (2003b) Reflections on glare. Lighting Research and Technology 35(2), pp.163-176

Wienold, L. and Christoffersen, J. (2006) Evaluation methods and development of a new glare prediction model for daylight environments with the use of CCD cameras. Energy and buildings, 38970, pp. 743-757