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Lighting for the Classrooms of the Future Electronic classrooms: a new challenge for school lighting guidance Tharinee Ramasoot Steve Fotios School of.

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Presentation on theme: "Lighting for the Classrooms of the Future Electronic classrooms: a new challenge for school lighting guidance Tharinee Ramasoot Steve Fotios School of."— Presentation transcript:

1 Lighting for the Classrooms of the Future Electronic classrooms: a new challenge for school lighting guidance Tharinee Ramasoot Steve Fotios School of Architecture University of Sheffield, UK

2 The Classroom of the Future Initiated by the Department for Education and Skills (DfES) in the UK in New ideas of designing learning environment for tomorrow, taking full advantage from Information and Communication Technology (ICT). Expansion in use of DSE (Display Screen Equipment) and other ICT interfaces which demands different lighting to traditional paper-based tasks.

3 Visual tasks in the Classroom of the Future Non-self-luminous & Self-luminous tasks –A variety of tasks carried out at the same time: may not be possible for simple solution such as dimming or switching. –Non self-luminous tasks: visual performance increase with ambient illumination up to the point of diminishing returns. –Self-luminous tasks: wash-out reflections and distracting reflections reduce users’ acceptability and visual performance. More light = better

4 Visual tasks in the Classroom of the Future Non-self-luminous & Self-luminous tasks –A variety of tasks carried out at the same time: may not be possible for simple solution such as dimming or switching. –Non self-luminous tasks: visual performance increase with ambient illumination up to the point of diminishing returns. –Self-luminous tasks: wash-out reflections and distracting reflections reduce users’ acceptability and visual performance.

5 Visual tasks in the Classroom of the Future Non-self-luminous & Self-luminous tasks –A variety of tasks carried out at the same time: may not be possible for simple solution such as dimming or switching. –Non self-luminous tasks: visual performance increase with ambient illumination up to the point of diminishing returns. –Self-luminous tasks: wash-out reflections and distracting reflections reduce users’ acceptability and visual performance. More light = worse

6 Visual tasks in the Classroom of the Future Individual screens Computer monitors e.g. LCDs, CRTs Limited viewing geometry Can be tilted to avoid reflections Shared screens Interactive whiteboards, projection screens, large screens e.g. plasma, LCDs. Viewed from various locations Fixed position -difficult to avoid reflections

7 Reflection components on DSE Diffuse (Lambertian): uniform, wash-out reflections that reduce contrast. Specular: distinct reflections that draw attention from tasks. Haze: combines properties of diffuse and specular components. not adequately addressed in current guidance.

8 Reflection components on DSE Proposed representation of reflection components (Arbitrary scale)

9 Reflection components on DSE

10 Survey of ICT classroom users Teacher responses (n=24) Pupil responses (n=134)

11 Survey of classroom environment Survey using a luminance meter and luminance mapping using WebHDR Wide variation of room surface luminances and sizes will impair readability of DSE. Small surfaces of high luminance, such as electric light sources and windows expected to cause problems of disturbing reflections.

12 Current guidance systems in the UK Luminance limits: 1500 cd/m² for DSE cat. 1, 2 and 500 cd/m² for DSE cat. 3 in positive polarity. Luminance limits: 1000 cd/m² for DSE cat. 1, 2 and 200 cd/m² for DSE cat. 3 Category 1, 2 and 3

13 How the current system works Display screen tests in current standards are based on the two principles: 1.“Legibility” of display : keeping the contrast (or luminance ratio) between character to background in presence of reflections above a certain level. (To prevent wash-out images) 2.“Acceptability” of disturbing reflections : keeping the contrast (or luminance ratio) between disturbing reflections to background below a certain level. (To prevent distracting reflections) CRT (BS9241-7) LCD (BS ) Positive polarity Negative polarity

14 How the current system works Display screen tests in current standards are based on the two principles: 1.“Legibility” of display : keeping the contrast (or luminance ratio) between character to background in presence of reflections above a certain level. (To prevent wash-out images) 2.“Acceptability” of disturbing reflections : keeping the contrast (or luminance ratio) between disturbing reflections to background below a certain level. (To prevent distracting reflections) CRT (BS9241-7) LCD (BS ) Positive polarity Negative polarity Preliminary studies suggest that higher luminances are tolerable in newer screens Tests using 1. extended light source (>15°) 2. small light source (1°) Tests are based on research in late 1980s

15 Pilot study 1: Higher luminance tolerable? Tests carried out at Zumtobel (UK) using the BS method and adapted equations (Howlett, 2003) to predict the maximum luminaire luminance to which a screen can be exposed without causing disturbing reflections. Many modern screens can tolerate much higher luminaire luminance limits than are currently prescribed. However, some screens predicted to tolerate higher luminance than standard suffer from clearly visible reflections under normal office lighting and in a dark room.

16 Three critical problems 1.The interactive whiteboard is the most common cause of visual problems yet is not addressed in current guidance. 2.The learner-centred mode of study means that simple solutions such as dimming the lighting across a classroom are no longer appropriate. 3.Evidence suggests that current guidance is out of date. The current limits on luminaire luminance are un- necessarily restrictive: higher luminances are possible without causing disturbance. Changes in screen technology have introduced new problems such as haze reflection. Glossy screen with high contrast can suffer from disturbing reflections despite meeting the criteria of BS EN ISO The guidance does not accommodate rapid changes in DSE technology.

17 Experimental work at Sheffield University 1.Determine the limits of luminaire luminance for the DSE that will be used in the Classroom of the future using DSE test methods prescribed in the current guidance. 2.Evaluate the acceptability of screen reflections using subjective testing, and hence identify limits of luminaire luminance.  Adjustment tasks  Rating tasks 3.Identify the effects of DSE type and luminaire luminance on task performance  Reading tasks 4.Determine how the system for predicting acceptable limits of luminaire luminance should be modified to correlate with subjective responses.

18 Experimental work at Sheffield University Adjustment tasks: The subjects perform reading tasks and adjust the luminaire luminance to identify the borderline. Similar to Hentschel et al. (1987), Pawlak and Roll (1990), Kubota and Takahashi (1989) Rating tasks: The subjects perform reading tasks and rate the acceptability of luminaire luminance levels. Similar to Hentschel et al. (1987), Pawlak and Roll (1990), Lloyd et al.(1996), Wang (1996), Miller et. al (2001) 5 screen types (1 CRT, 2 LCDs, 2 WBs) x 2 sizes of glare sources (1°,10°) Identify acceptability thresholds using three visual criteria: Disturbance: Very disturbing – Not at all disturbing Contrast: Highly unacceptable - Highly acceptable Clarity: Hazy (Very blurred)- Focus (Very sharp) Identify limit of luminaire luminance using two subjective methods similar to previous studies, including studies that British Standards are based on.

19 Experimental work at Sheffield University Adjustment tasks: The subjects perform reading tasks and adjust the luminaire luminance to identify the borderline. Similar to Hentschel et al. (1987), Pawlak and Roll (1990), Kubota and Takahashi (1989) Rating tasks: The subjects perform reading tasks and rate the acceptability of luminaire luminance levels. Similar to Hentschel et al. (1987), Pawlak and Roll (1990), Lloyd et al.(1996), Wang (1996), Miller et. al (2001) 5 screen types (1 CRT, 2 LCDs, 2 WBs) x 2 sizes of glare sources (1°,10°) Identify acceptability thresholds using three visual criteria: Disturbance: Very disturbing – Not at all disturbing Contrast: Highly unacceptable - Highly acceptable Clarity: Hazy (Very blurred)- Focus (Very sharp) Reading tasks: The subjects read at their maximum reading speeds to determine visual performance. Objective measure of how screen type and light source affect task performance – alternative method to find luminaire luminance limits

20 Proposed new system of specification Subjective measures Adjustment tasks & Rating tasks Objective measure Reading speed task Current system of guidance Lighting recommendations for DSE uses BS EN , BS EN ISO SLL’s Lighting Guide 3, 7 Method for DSE classification Based on reflection tolerance BS EN ISO (CRTs) BS EN ISO (FPDs) Minimum qualities of DSE to suit the lit environment Luminance, Contrast, Reflection (diffuse, specular, haze) Lighting requirements for all Visual tasks in classroom Non-self luminous visual tasks Self-luminous visual tasks Revised system of guidance Display parameters - Luminance - Luminance contrast - Reflection parameters User responses - Acceptability of screen reflections - Performance Lighting parameters -Luminance - Illuminance - Luminous intensity Lighting-display interaction

21 Thank you Tharinee Ramasoot Steve Fotios School of Architecture University of Sheffield The Arts Tower, Western Bank Sheffield, S10 2TN, United Kingdom

22 Pilot study 2: Adjustment and rating tasks To compare reflection acceptability thresholds using three visual criteria –Disturbance –Contrast –Clarity To investigate effects of –Luminance –size of glare source –screen polarity To compare results from two test methods –Adjustment method –Rating method Pilot adjustment task: CRT only 2 x polarity (positive, negative) 5 x size (1°,5°,10°,15°,20°) 2 subjects, each did 12 trials of all 10 conditions for 3 criteria Pilot rating task: 2 x screen (LCD and CRT) 2 x polarity (positive, negative) 5 x size (1°,5°,10°,15°,20°) 4 x luminance level (200, 500, 1000, 2000 cd/m²) 2 subjects, each did 5 trials of all 80 conditions for 3 criteria

23 Pilot study 2: Setting

24 Pilot study 2: Results Results show that luminance levels at three acceptability thresholds are different and typically in the order: Disturbance threshold < Contrast threshold < Clarity threshold Effects are also found from –Size of glare source: lower luminance thresholds with increasing size of glare source. The effect is smaller as the size increases above 10°. –Display screen polarity: lower luminance thresholds for negative polarity. –Screen type: CRT got lower average ratings than LCD under same light conditions.

25 Pilot study 2: Results Results from adjustment task and rating tasks are well-matched. Average threshold values from adjustment task are relatively similar to rating =5 or 5.5 in rating task. The adjustment and rating tasks will be used in main tests with 5 types of DSE 2 luminaire sizes (1° and 10°) 2 polarities 3 visual criteria

26 Pilot study 3: Reading speed tasks To determine controlled reading parameters for the main test: –Length of reading materials (unrelated words chosen from primary-school vocabulary) –Difficulty of reading materials: Difficulty of the 10 versions of reading materials randomly used in the test should be similar. Pilot reading task A: length of reading materials 20 subjects, 7 text lengths (10,20,30,40,50,75 and 100 words) Subjects read at their maximum speed Pilot reading task A: difficulty of reading materials 20 subjects, 10 versions of text (10,20,30,40,50,75 and 100 words) Subjects read at their maximum speed

27 Pilot study 3: Results Reading rate was consistent for tests with 50 words and above. Therefore reading test will use 50 unrelated words.

28 Pilot study 3: Results ANOVA result showed that the reading speed was not significantly affected by test versions, F(9,171)=0.424, p= Therefore any version of the text could be randomly used in the reading test to without significantly affecting the reading speed.


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