【摘 要】
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Projector-aided multimedia teaching is becoming more and more popular in numerous school classrooms in China.At the same time,teachers and students increasingly complain about limited visibility and v
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Projector-aided multimedia teaching is becoming more and more popular in numerous school classrooms in China.At the same time,teachers and students increasingly complain about limited visibility and visual comfort of projection screens,raising concerns on eye care in schools.The aim of our study was to first investigate the current lighting conditions in classrooms when watching a projection screen,and then to search for lighting conditions providing optimal visibility and visual comfort.A survey was carried out to collect desk illuminance,projection screen luminance and contrast from eight schools in four cities in China.Based on the survey,an experiment was designed and performed with three ambient illumination conditions (i.e.,0lux,300lux,daylight),five different projection screen luminance levels (i.e.,50,100,150,200,260 cd/m2),five seating positions and two font sizes (i.e.,18,24).Twenty two students participated in the experiment.Under each ambient illumination condition,the students were asked to tune the contrast of the letters on the projection screen to 1) a value that corresponded to the visibility threshold of the letters,and 2) a value that corresponded to a comfortable threshold for reading the text.The results indicate that the ambient illumination,the projection screen luminance,the seating position and the font size all have a significant influence on the visibility of text on the projection screen and on visual comfort.To provide comfortable lighting to students using a projection screen,its luminance should be above 100cd/m2,the desk illuminance should be 300lux and a perceived projection screen contrast should be above 0.5.
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