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Dates: January 2006–2010
Staff: Steve Fotios, Tharinee Ramasoot, Rosie Parnell
Funding: EPSRC ref EP/F029276/1; Lighting for the classroom of the future: Acceptability of glare; S Fotios & R Parnell, May 2008 to April 2009.
Thorn Lighting.
Royal Thai Government PhD scholarship.
A new model for predicting the acceptability of disturbing reflections on display screens
A new model for predicting the acceptability of disturbing reflections on display screens
The Classroom of the Future was a DfES programme to explore the design of classrooms for the 21st century where information and communication technology (ICT) will be more extensively used. This study commenced by investigating appropriate lighting for these classrooms
Preliminary research included a survey of classroom lighting problems using questionnaires distributed to classroom users and designers; an analysis of visual tasks in classroom using visual performance models; and a review of current lighting guidelines and their underlying principles. This work revealed three critical problems:
The learner-centred mode of study, in which students work on a variety of self-paced tasks, means that simple solutions such as dimming the lighting across the whole of a classroom are no longer appropriate.
The interactive whiteboard is the most common cause of visual problems with reflections, yet is not addressed in current guidance. One issue is that the whiteboard is observed from a greater range of viewing angles than are personal work stations.
There is some evidence to suggest that current guidance for DSE environments, BS EN 12464-1:2002, SLL Lighting Guide 7, are out of date: (i) The current limits on luminaire luminance are un-necessarily restrictive (e.g. 1500 cd/m2 for type I positive polarity display); following improvements in DSE technology, higher luminances are possible without causing disturbance. (ii) Changes in screen technology, such as the use of antiglare coating, have introduced new problems such as haze reflection which are not adequately addressed in guidance. Glossy screens are popular for their high contrast but can suffer from disturbing reflections despite meeting the criteria of BS EN ISO 13406-2:2001 and BS 9241-7:1998. (iii) The guidance does not accommodate rapid changes in DSE technology.
Funding was awarded by the EPSRC to investigate the acceptability of glare on screens: what are acceptable luminances on different screens before these are considered to be disturbing or to affect work. Three tests were carried out. Two of these were subjective assessments, using the adjustment task and the category rating task, to identify the luminance of the disturbance threshold. The third test used a reading speed task to provide an objective measure of the effect of screen reflections.
The results below, from the adjustment task, show luminances at the disturbance, contrast and clarity borderlines tested with the 10° light source at 15° viewing angle, showing the luminances satisfactory to 95% of participants with each of the seven screens that were tested. It can bee seen that different screens exhibit different luminance thresholds: the matt LCD screen (LCMP) can tolerate high luminaire luminance before the reflection becomes disturbing but the glossy LCD screen (LCGP) can tolerate only a low luminance. Such variation is not accounted for in current guidance as to limits of luminaire luminance.
A stepwise regression process used to obtain a model for predicting the results of the adjustment task:
where:
LA = Disturbance borderline luminance (cd/m2)
ρs = Specular reflectance for the particular size of light source
H = Effect of haze reflection
LB = Background luminance of the display screen (cd/m2)
Ω = Area that the reflected light source subtends at the viewing position (sr)
This model can explain up to 86% of the variance in Log10LA.
Publications
Publications
Ramasoot T and Fotios SA, Lighting and display screens: models for predicting luminance limits and disturbance, Lighting Research & Technology, 2012; 44(2); 197-223.
Lighting Guide LG5: Lighting for education. London: The Society of Light and Lighting (SLL/CIBSE); 2011. ISBN 978-1-906846-17-6. (Fotios and Ramasoot were members of the task group lead by Iain Macrae)
Fotios S and Ramasoot T, New lighting recommendations for the classroom of the future based on luminous parameters of display screen equipment. Journal of Light and Visual Environment, 2010; 34(3); 165-169.
Fotios S and Ramasoot T, Developing a model to predict user acceptability of display screen reflections, Lux Europa, Istanbul, 2009, 513-520.
Ramasoot T and Fotios SA, Lighting for the Classrooms of the Future. Electronic classrooms: a new challenge for school lighting guidance, Light & Engineering, 2009; 17(2); 62-70.
Ramasoot T and Fotios S, The model of DSE user acceptability and performance: the derivation of new lighting recommendation for the classroom of the future. PLEA 2009, Quebec, June 2009, 269-274.
Ramasoot T and Fotios SA, Lighting for the classrooms of the future. Electronic classrooms: a new challenge for school lighting guidance, Svetotekhnika, 2009; 2; 28-34.
Fotios S and Ramasoot T, New lighting recommendations for the classroom of the future based on luminous parameters of display screen equipment, Proceedings of the 6th Lux Pacifica, Bangkok, 23-25. April 2009, 131-134.
Ramasoot T and Fotios SA, Acceptability of screen reflections: lighting strategies for improving quality of the visual environment in classrooms of the future, PLEA 2008, Dublin, October 2008.
Ramasoot T and Fotios SA, Lighting for the classrooms of the future. electronic classrooms: a new challenge for school lighting guidance. Balkan Light 2008, Ljubljana, Slovenia, 7–9 October 2008, pp59-68.
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