Address:
Lighting Research,
Sheffield School of Architecture,
University of Sheffield,
Arts Tower, Western Bank,
Sheffield,
S10 2TN.
Telephone: +44 (0) 114 222 0371
Email:
steve.fotios@sheffield.ac.uk
Current researchers:
Steve Fotios
Chris Cheal
Deniz Atli
Jemima Unwin
Biao Yang
LumeNet 2012:
A workshop for PhD research students of the art and science of lighting ... 19th-21st June 2012
April 2012
We have recently made good progress on four projects. Three of these relate to the MERLIN project investigating lighting for pedestrians. We have:
- Finished gathering data on pedestrians evaluation of reassurance (i.e. perceived safety) when walking at night-time. The aim of this work is to identify whether lighting matters for reassurance (further work will investigate characteristics of light) and the challenge was to gather these data without priming respondents about lighting, fear or safety, and without lighting being the obvious item of attention.
- One issue we are studying is inter-personal judgements made about the intent and identity of other pedestrians. Past work has focussed on facial recognition but we do not consider this to be the appropriate target. A brief pilot study has sought to identify what features of other people we can identify at different distances.
- The outcome of MERLIN is to propose appropriate design illuminances for pedestrian lighting. A study of obstacle detection was carried out to explore approaches to setting illuminances based on visual needs, noting of course that there are forces beyond visual which contribute to illuminance standards. One approach was to identify the point of inflection in the relationship between illuminance and obstacle detection – these parameters exhibit a plateau-escarpment relationship so the knee in this curve identifies an optimum point. The second approach was to identify what size target we should expect a pedestrian to detect and with what probability.
Work has progressed in characterising the effect of lamp spectrum on spatial brightness at photopic levels. We have finalised the review of past studies of spatial brightness to identify the evidence that gives reliable estimates of the magnitude of the spectrum effect. The first stage of analysis has been to use data from matching and discrimination tests (as these give the magnitude and direction of the effect) to screen potential metrics for brightness, e.g. the S/P ratio (the basis of Berman’s brightness lumens), gamut area, colour metrics such as CCT and CRI, and models of equivalent luminance. Initial analysis suggests ratios of gamut area and ratios of (S/P)0.5 give the better predictions of the metrics examined: perhaps a combination of these two will show an improvement. Any metrics proposed will next be validated by experiment, using side-by-side matching and separate-evaluation rating procedures.
LumeNet 2012 is rapidly approaching and we are making plans to ensure it is an interesting and worthwhile event for the 40 PhD students we are expecting. Looking forward to meeting all who attend.
October 2011
The school of architecture has recently moved backed to the Arts Tower and a first task for the lighting group is setting up the laboratory rooms. Biao Yang has started work on his PhD regarding judgement of intent : what is it that a pedestrian uses to interpret the intent of other pedestrians? We suspect it is more than simple facial recognition. He has already found some interesting ideas, for example, questioning the basis of Hall's personal proximity limits. Jemima Unwin has carried out a pilot study of reassurance , our expression for perceived safety or fear of crime, and from this is revising the procedures for a principal study that will take place in the coming winter. Her main question is: does lighting contribute to reassurance? Some past studies have suggested so, but in the context of other social and environmental factors the effect is questionable. Chris Cheal is setting up the obstacle detection apparatus to examine the effect of luminance on detection probability: the pilot study results suggested a plateau-escarpment relationship, as exists with RVP at higher light levels, but with only three light levels in the pilot study we must question whether it was an experimental artefact. If the plateau-escarpment transition is real, however, this would provide a useful clue as to minimum light levels for pedestrian lighting. Deniz Atli has had a successful first year in her PhD studying spatial brightness : she has completed a review of studies using the category rating method, along the way publishing articles on response-points in rating scales and a comparison of brightness and clarity ratings, and is now starting a regression analysis of metrics which might predict how lamp spectrum effects spatial brightness.
LumeNet 2012 : this is a conference / workshop for PhD students studying lighting – themes within lighting, daylighting, colour and vision are welcomed. Students will present their work, in particular the methods they intend to use for experimental work, and will receive critical feedback from a group of experts who will attend the event – this includes John Mardaljevic, Jens Christoffersen, Peter Boyce, Mike Pointer and Jennifer Veitch. LumeNet takes place on 19-21 June 2012 at the University of Sheffield – please register soon if interested. Thanks to VELUX, Thorn Lighting, Zumtobel Lighting and the Society of Light and Lighting for their sponsorship. LumeNet 2012 >>
March 2011
March is the official start of the MERLIN project at Sheffield and we have been joined by a new PhD student, Jemima Unwin, who will investigate reassurance in streets at night-time - does lighting have any effect and, if so, what characteristics matter? Jemima is an architect who has international experience having worked for practices in Kyoto, Sydney, Manchester & London. Her architectural education was completed at the Mackintosh School of Architecture in Glasgow and Ecole d'Architecture de Paris-Belleville in Paris. Her long term interest in both electric and day lighting was formalised in the completion of the MSc in Light & Lighting at UCL in 2010, after which she was awarded the prestigious Millar Award by the Worshipful Company of Lightmongers. She is excited to join such a fascinating project which involves understanding how lighting affects people’s experience of their urban environment.
A second PhD student, Biao Yang, is expected to start in summer 2011: Biao is currently completing his masters study with Yandan Lin at Fudan University. His work will investigate recognition of facial expression under different types of street lighting. Previous work in this area has tended to investigate the identification of faces and has allowed continuous scrutiny of the target face. This is probably not the right approach. The task for pedestrians is more likely to be determination of whether the person is friendly or not: the psychology literature suggests investigation of expression rather than identification may give a better clue as to whether or not the person should be avoided, and early results from the eye tracking survey at UCL (Peter Raynham and Navaz Davoudian) suggest that the scanning of a face is carried out in a very brief time rather than continuous scrutiny. A new methodology has been proposed (Fotios & Raynham, Lighting for pedestrians: Is facial recognition what matters? Lighting Research & Technology 2011; 43/1: 129-130).
November 2010
Tharinee Ramasoot submitted her PhD thesis (Investigation of Lighting and Disturbing Reflections on Display Screens: A New Model for Judging Acceptability); this was examined by Peter Boyce and was accepted with only very minor corrections. Well done Tharinee! Her work contributed to the revised SLL guidance for lighting in classrooms. She has now returned to Silpakorn University, Bangkok to resume her lectureship.
We have been joined by a new PhD student, Deniz Atli from Turkey. Deniz previously studied at Bilkent University, completing her undergraduate degree in the Department of Interior Architecture and Environmental Design and her Masters degree in Architectural Lighting. Her Masters thesis examined the effects of colour and coloured light on depth perception, comparing different colour combinations of backgrounds with objects, and with this focus on visual perception she is an ideal new colleague for the research group at Sheffield. Deniz will be studying lamp spectrum and brightness perception in interior spaces.
On-going projects: development of a new method for measuring facial recognition under different road lighting conditions; examination of the method of adjustment (i.e. dimming) for setting preferred levels of illuminance or CCT.
July 2010
We received the good news from EPSRC that the MERLIN project (Mesopically Enhanced Road Lighting: Improving Night-vision) was approved for funding. This is a collaborative project with John Barbur at City University and Peter Raynham at UCL with a total value of over Ł1 million. Our intention is to find out what visual tasks are critical for pedestrians at night-time, how these tasks are affected by the amount, spectral distribution and spatial distribution of light, and thus set design targets for pedestrian lighting.
PhD studentships. The funding awarded to Sheffield University for MERLIN includes two PhD studentships covering fees (UK/EU residents) and a student bursary for three years. These are likely to start in February and June 2011. Please contact us if interested.
April 2010
It has been a busy start to the year, with presentations delivered at Stockholm Lighting Days and the CIE 2010 conference in Vienna, a new model developed to predict disturbing reflections on display screens, new data emerging on spatial brightness at mesopic levels, progress with the CIE and ILE committees tasked to consider spectral power characteristics of lighting at mesopic levels, and a new technical committee set up within the CIE to examine research methods.
In February, Navaz Davoudian's PhD thesis was examined by Prof. Stephan Völker of the Berlin Institute of Technology: we are pleased to report that she passed, subject only to minor corrections.
Tharinee Ramasoot has developed a new model for predicting the threshold luminance to avoid disturbing reflections on display screens. This model is based on results of an experiment using luminance adjustment to find the disturbance borderline; the experiment used seven different screens including interactive white boards, three sizes of reflection, and two viewing locations. The results were validated using a second methodology (category rating at a series of fixed luminances) and through comparison with previous data and models. Tharinee is due to submit her PhD thesis in June 2010 and this will be examined by Peter Boyce.
The brightness matching trials being carried out by Chris Cheal are nearly complete. These trials are carried out at mesopic levels, providing data to aid the selection of optimum characteristics for lighting in residential roads. A critical issue these data reveal is that some lamps which create spaces that appear to be very bright do not give pleasing appearance of skin or a colour array; a compromise is needed. BS5489-1:2003 allows the illuminance of lighting in residential roads to be reduced by one class of the S-series when using lamps of Ra>60. These new brightness data, together with our previous work on obstacle detection, suggest the illuminance reduction should be allowed for lamps having both Ra>60 and S/P>1.6 (this is a first estimate, to be reviewed on completion of trials); Ra correlates with preferred appearance of skin and colours; S/P ratio correlates with brightness judgements and visual performance.
We were pleased to receive in January a visit from Ásta Logadóttir of the Danish Building Research Institute. She is carrying out a study of preferred illuminances and CCTs in an office setting and this meeting gave us a chance to share ideas on methods.
A new technical committee has been set up within the CIE, TC 1-80: Research Methods For Psychophysical Studies Of Brightness Judgements. The terms of reference are: To report on research methods (both research design and statistical analysis) for psychophysical studies of spatial brightness judgements. The aim is to bring best practices from psychology into the wider awareness of people in the lighting community who wish to use such tools in their own work, to avoid errors that plague the existing literature. Steve Fotios is the chairman of this committee - please contact if you would like to participate.
November 2009
Navaz Davoudian is about to submit her PhD thesis: she has examined how the saliency of an object is affected by the background pattern of lighting. If lighting master plans were able to control background lighting this would enable luminance contrasts to be reduced for the same level of saliency. Navaz has recently started a new research post at UCL, working with Peter Raynham.
Tharinee Ramasoot is working through the results of the screen glare tests. She gathered an immense amount of data so this analysis will take a while to complete. The results show that there is a wide variance in the luminaire luminance that can be tolerated by different screens before the reflections become disturbing. A new system of guidance may be needed to deal with this, and to future proof guidance against further changes in DSE technology.
Chris Cheal has set up the brightness matching apparatus. We have chosen five different lamps for these trials, these being used in all possible pairs, and this will enable predictions of brightness based on conventional lamp colour metrics to be tested. The tests will mainly use the brightness matching procedure backed up by a forced choice judgement at equal illuminance; foveal visual performance will be tested using a low contrast acuity chart, and preference of skin appearance will be examined.
Steve Fotios is chairman on the new ILE Mesopic Vision panel. This has been set the task of providing road lighting designers with guidance on application of new research of mesopic vision. He is also setting up a proposal for a new CIE technical committee to examine research methods for subjective evaluation of lighting.
June 2009
Brightness of Street Lighting: over the past year we have carried out brightness matching trials to verify the results we gained from a previous study using side-by-side matching. In one set of trials we repeated the side-by-side match but used a range of different field designs, from a neutral uniform surface to an interior space with coloured surfaces: there was little effect on the illuminance ratio at equal brightness. A second study used sequential evaluation (lighting from two different lamps used in temporal succession to illuminate a single space) rather than the simultaneous (side-by-side) evaluation used previously: there is negligible difference between the illuminance ratios at equal brightness derived from the two methods. These findings provide support for continued use of the side-by-side matching task. We are now setting up a series of trials to identify a lamp quality metric for specifying when it is acceptable to reduce the illuminance of street lighting.
Disturbing Reflections: Three methods have been used to evaluate the effect of light sources reflected in display screens including interactive whiteboards. Two of these were subjective evaluations, using an adjustment task and a rating task to identify the luminance of the disturbance threshold. The third was a reading speed task, to provide an objective measure of the effects. Analysis of the results to date shows a wide variation of disturbance threshold luminances between different types of screen, and that these luminances are not well specified in current British Standards. We are proposing an alternative system, in which minimum qualities of display screen are specified to meet the characteristics of the installed lighting rather than vice versa as is the current situation. Specifying minimum qualities of display screens rather than limiting qualities of the lighting provides a way of future-proofing lighting guidance.
Wayfinding: Alison Chang was awarded her PhD thesis for a study of spatial attributes of buildings and reassurance when way-finding. We intend to extend this work to investigate effects of lighting on reassurance for pedestrians at night-time.
March 2009
Chris Cheal has constructed a new apparatus for sequential brightness matching tests. We will be using this to see how the results compare to previous matching tests using simultaneous evaluations (side-by-side presentation). The recent study of field design suggested the addition of coloured surfaces or objects into the visual field does not have significant effect on the matching task. Tharinee Ramasoot is setting up the screen reflection apparatus to use the rating method of subjective evaluation, and these results will be used to confirm those previously gained using the adjustment task. Steve Fotios published an article in the IESNA journal Leukos discussing the category rating method for judging the brightness of lighting: many studies have used this method to compare lighting of different spectral power distribution and this article offers an explanation for why some studies report a significant effect yet others suggest negligible effect.
January 2009
RAE2008: The School of Architecture performed very well in the 2008 Research Assessment Exercise. Within the Architecture and the Built Environment unit we are ranked joint first or joint third (depending on the method used to interpret the quality profile) out of the 35 universities who submitted.
Tharinee Ramasoot has finished the first stage of the screen reflection tests, an adjustment task using younger subjects and seven types of display screen. These initial results show that some screens can tolerate much higher luminaires luminances than are permitted under the current systems of specification.
Chris Cheal is conducting tests to examine how the brightness matching task is affected by design of the illuminated field, and these range from a uniform surface to a space furnished to simulate a residential street. This preliminary work is needed to guide the design of experiments we will conduct to compare spatial brightness from lamps of different SPD.
October 2008
Two series of tests are about to start: evaluations of reflections on display screens and brightness matching at mesopic levels using a wide range of lamp SPD. Both of these are EPSRC funded projects. Presentations were given by group members at several conferences through the summer - Balkan Light 2008, PLEA 2008, ILE annual conference and the SLL/LR&T seminar. Steve Fotios will be attending the IESNA annual conference in November to work with the visual effects of lamp spectral distribution committee. Steve was chairman of the team drafting ILE technical report TR29: White Light, and this was launched at the ILE annual conference.
June 2008
The obstacle detection research found that lamp type affects the detection of pavement surface irregularities at low illuminance (0.2 lux) but not at higher illuminances (2.0 and 20 lux), and for the three lamps tested the effect is as predicted by S/P ratio - the higher the S/P ratio, the better the ability to detect small obstacles. The final report will be available from this website.
February 2008
Prof. Peter Tregenza, Prof. Peter Boyce and Andrew Gooding of Urbis Lighting attended an ideas workshop at Sheffield University to discuss the new research projects - Lighting for the Classroom of the Future and A Metric for Specifying White Light. This meeting lead to interesting ideas for improving the proposed research strategies; for example, the street lighting tests will now include assessment of skin appearance under different lighting in addition to the proposed brightness and visual performance tests.
Steve Fotios has commenced drafting the ILE technical report providing evidence in support of white lighting in subsidiary streets. He is chairman of the panel that also includes Nigel Townsend (Urbis Lighting), Kevin Moss (West Sussex County Council), Mark Hooper (Lighting & Electrical Design Services Ltd) and Alistair Scott (Design for Lighting). The report is due to be published in time for the ILE annual conference in Bristol, September 2008.
December 2007
EPSRC funding for two research projects was awarded to Dr Fotios:
- Lighting for the classroom of the future: Acceptability of glare (EPSRC ref EP/F029276/1)
- Street Lighting: A metric for specifying white light (EPSRC ref EP/F035624/1)
September 2007
Chris Cheal was awarded his PhD for a thesis on street lighting and lamp SPD. It was examined by Peter Raynham of UCL.
Steve Fotios received the Institute of Lighting Engineers (ILE) award for best presentation at the 2006 ILE National Conference. This presentation discussed the use of whiter light sources for lighting in residential streets, a project funded by EPSRC.
Steve Fotios has been nominated as Chairman for the brightness sub-committee of the IESNA (Illuminating Engineering Society of North America) Effects of Lamp Spectral Distribution committee. The committee constitution has been revised by the chairman, Brian Liebel, to investigate SPD effects at photopic conditions whereas it was previously concerned only with mesopic conditions.
May 2007
Project agreed with Colette
Knight, Philips Lighting Ltd., to investigate obstacle detection under
different types of light source. Obstacle detection is one of the primary
visual tasks of pedestrians, and has not previously been directly tested.
Received the Leon Gaster Award 2006 from the Society for Light & Lighting
for an article in Lighting Research & Technology: Fotios SA, Cheal C & Boyce
PR, Light Source Spectrum, Brightness Perception and Visual Performance in
Pedestrian Environments: A Review, Lighting Research & Technology, 2005;
37(4); 271-294