s light in all directions (diffuse reflection) no glare spot Extent of glare related to the ratio of diffuse to specular (mirror-like) reflection

Aims To what extent are pupils exposed to 100Hz flicker? To what extent are pupils exposed to lighting that can promote glare through: –Illuminance at pupils’ desks –Luminance of whiteboards

Methods

Sample 90 classrooms 11 secondary schools 6 local authorities Sampling Random Stratified across LA’s, schools, buildings, curriculum areas Lighting conditions: lights on/blinds up; lights off/blinds up; lights on/blinds down/lights off/blinds down July, Aug, Sept 2006

Flicker Servo-controlled rotating shutter set to 104 occlusions per second Lamps which flickered at 100Hz appear to be flashing at a 4Hz beat4Hz beat

Illuminance Illuminance assessed with lux meter Sampling positions distributed evenly across the room Extent to which teachers can control illuminance assessed through –functional state of blinds –functional state of lighting and versatility of control

Whiteboards Standardised image projected onto board Luminance measured with spot photometer –within and outside glare spot –against black stripe and white background Measured in classrooms and under lab conditions –Contrast within and outside glare spot [Michelson contrast = Lmax-Lmin/Lmax+Lmin] –Ratio of specular to diffuse components of reflection

Results

Flicker 20% of classrooms lit solely by ~32kHz In remaining 80% of classrooms, mean of 90% of lamps flickered at 100Hz

Illuminance Within classrooms, large variation in mean illuminance at pupils’ desks: –Inadequate: Min 38 lux –Excessive: Max >2500 lux (limit of the meter) Mean illuminance across classrooms exceeds recommendations –1168 lux (blinds open, lights on) –807 lux (blinds open, lights off) –684 lux (blinds closed, lights on) Illuminance in excess of 1000 lux in 84% of classrooms (lights on, blinds open) and 40% of classrooms (lights on, blinds closed)

What causes high illuminance? Daylight contributes more than fluorescent lighting to net illuminance. In classrooms with functioning blinds: –Mean illuminance (lights off-blinds open) > mean illuminance (lights on-blinds closed) –Mean illuminance significantly related to window area –No significant relationship between mean illuminance and number of fluorescent lamps with lights on-blinds open, but there was a significant relationship when blinds closed

What causes high illuminance? Illuminance from fluorescent lighting is unnecessarily high –In 60% of classrooms with functioning blinds, minimum illuminance was above 300lux with lights on, blinds closed Significant relationship between local authority and mean illuminance

Teachers’ control of illuminance: blinds Blinds absent in 23% of classrooms In 51% of those with blinds, at least one was missing or malfunctioning Mean of 1.4 blinds per classroom absent or malfunctioning, affecting mean of 39% of window area Mean illuminance still in excess of 300 lux in 24% of classrooms with lights off, blinds closed (81% with blinds open)

Teachers’ control of illuminance: fluorescent lights Association between number of lamps and floor area, but no relationship with window area Yields excessive illuminance in well day-lit areas Compensation for excessive daylight by selectively switching off lamps impossible in 27% of classrooms Only 2 classrooms had automatically dimming lamps Mean of 5% of lamps per classroom were broken or missing

Whiteboard luminance With one exception, all whiteboards were vertically mounted, directing specular reflection into pupils’ eyes

Whiteboard luminance Maximum luminance (DWB) – cd/sqmetre (lights on, blinds open) Significant differences between IWBs and DWBs –Mean (DWB) cd/sqmetre –Mean (IWB) 1032 cd/sqmetre Significant differences between IWB brands –Brand 1: Mean 376 cd/sqmetre –Brand 2: Mean 1850 cd/sqmetre –Both brands are market leaders and were the extremes for IWBs.

Effect of luminance on whiteboard contrast Ratio of specular reflection to diffuse reflection –Brand –Brand Effect on contrast –Brand (outside glare spot), 0.91 (inside glare spot) –Brand (outside glare spot), 0.53 (inside glare spot) These findings appear to be associated with extent of visible sheen. Significant differences in luminance between IWBs with visible sheen and no sheen –Sheen: mean luminance 1440 cd/sqmetre –No sheen: mean luminance 376 cd/sqmetre

Effect of illuminance on whiteboard contrast Measured away from the glare spot… Highest whiteboard contrast with lights off-blinds down Such illuminance too low for adequate illumination of pupils’ desks (mean 198 lux) Lights needed to be on in 70% of classrooms to give just half of recommended paper luminance of 70cd/sqmetre, hence reducing whiteboard contrast Boards with a visible sheen are more susceptible to the effects of ambient lighting

Discussion

Summary Lighting in classrooms is consistent with conditions which can impair performance and promote discomfort –Flicker –Glare caused by excessive lighting –Glare from whiteboards & data projectors

Is flicker relevant to children? In adults, 100 Hz flicker impairs reading accuracy & visual performance and causes discomfort (Wilkins et al. 1989; Kuller & Laike 1998; Jaen et al. 2005) Younger individuals have higher CFF: maximum rate at which intermittent light can be perceived as flicker) (Lindner & Kropf 1993) People with higher CFF  more likely to complain about flicker (Brundrett 1974) Physiological responses are equally likely in children

Teachers and pupils prefer day light to fluorescent light (Galasiu & Veitch 2006) Teachers prefer to control the balance between fluorescent and day lighting (Lang 2002) Children’s behaviour differs between fluorescent and day lighting (Treichel, 1974; Fenton & Penney 1985) Learning and attainment differs between fluorescent and day lighting (Heschong et al. 1999; Heschong & Knecht 2002)

Implications for policy & practice Controlled studies of the effects of flicker on children’s visual performance and discomfort in school Relevant classroom measures of visual performance Relevant classroom measures of discomfort Implications for research Consider replacement of 100 Hz fluorescent lamps Exploit day light where possible, but avoid excessive illuminance

Illuminance Illuminance varies from inadequate to excessive Illuminance exceeds recommendations and is adequate to cause –disability glare at pupils’ desks. –discomfort glare (Rea 1982, 1983) Causes include excessive artificial lighting and poor control of day lighting

Is illuminance relevant to children? Glare is glare Teachers prefer soft lighting (Estes 1984) Behaviour better under soft lighting (Dinsmore 2003) May explain benefits of coloured overlays for some students as they reduce page luminance by half (Wilkins 2003) Implications for policy & practice Responsive control of fluorescent and day lighting Teachers usually don’t respond to current lighting, more to perceptions developed over time (Galasiu & Veitch 2005) Automatic control of lighting useful alternative

Glare from whiteboards Discomfort –Exceeded luminance recommended for paper i.e. 70 cd/sqmetre –Exceeded user preferences identified by van Ooyen et al. 1987) i.e cd/sqmetre –Magnitude of DWB luminance distinct discomfort

Glare from whiteboards Disability –Varies with extent of visible sheen (ratio of specular to diffuse reflection) –Boards with visible sheen: smoother surface compatible with dry-wipe markers, more specular reflection, more visible glare spot which reduced image contrast by half, more susceptible to reduction of contrast by ambient lighting, necessitating excessively low illuminance at pupils’ desks

Implications for policy & practice Presence of a visible sheen should inform purchasing decisions Don’t project onto a dry-wipe whiteboard as most susceptible to contrast reduction Re-angle boards upwards so specular reflection reflected to ceiling Use a coloured background