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Lighting Levels Affect Worker Preference and Productivity

Subjects who could control the level of illuminance at their assembly workstations had significantly greater productivity (4.5%) than those with a fixed workstation lighting level according to a field study by Juslén et al.  Also, study volunteers appeared to have preferred lighting levels – when the rate of dimming caused by a remote control was changed, subjects changed the duration they pushed the remote’s button (5.1 seconds with slow dimming compared to 3.3 with fast dimming).


There was a slight correlation between level of illuminance and productivity. 


The motive for a volunteer choosing a specific lighting level was not assessed but the authors suggest it could be visual (the need to see better) or psychobiological (mood).   


Study Design

Set Up and Variables Tested

Ten assembly workstations were equipped with a task-lighting system (two luminaires placed at a height of 1.24 meters above the work surface) which could be varied in level of illuminance through use of a two-button infrared remote control.


The study was conducted in two phases over its 15 month duration with changes made to (1) the frequency of needing to re-set the lighting level and (2) the remote dimming speed:

·         For approximately the first 7 months:

v      every hour, task lighting was switched off; the volunteer would restore lighting to the preferred level using the remote 

v      maximum illuminance could be acquired with the remote in 6.5 seconds (considered medium dimming speed)

·         For approximately the following 8 months:

v      at the beginning of breaks (three a day), task lighting was switched off; the volunteer would restore lighting to the preferred level using the remote

v      dimming speeds were randomly altered on a covert basis with maximum illuminance obtained in either 5 seconds (considered fast speed) or 9 seconds (considered slow speed)


The subjects could change the task-lighting level at any time.  Approximately 100 lux of surface light from the task-lighting system was produced when the remote was initially turned on.  General factory lighting produced a worksurface illuminance of 100 to 380 lux.  The task-lighting could contribute up to an additional 3000 lux.  Lighting at one workstation did not impact lighting at other workstations.  The minimum, maximum, and average lighting level was recorded for every 10 minute duration.


The tasks at the workstations were similar – assembling standard light products that included the frame, gear, optical parts and occasionally the cover. 



Fourteen volunteers participated in phase one of the study (first 7 months) while 8 subjects from the original 14 person group continued on to be involved with the experiment’s second phase (following 8 months). 


Control Group

Seven volunteers performed similar tasks at similar workstations illuminated with an unadjustable lighting system that produced 700 lux at the worksurface.  These employees worked in a separate area from the experimental group.


Productivity Measurements

The number of products produced in one hour became the unit of productivity measurement (“standard working hour”).   For the year prior to the experiment, the “standard working hour” production level was calculated for each subject.  The average “standard working hour” values of the phase 1 experimental group, phase 2 experimental group, and the control group were compared to the average “standard working hour” values produced by each group respectively in the year prior to the experiment.  


Other Findings

When the change in dimming was slow, the average illuminance preferred by subjects was 1183 lux while 1359 lux was the preferred illuminance when the change in dimming was fast.  The authors felt this 13 percent difference was nearly imperceptible and likely had little visual or biological impact. 


No correlation was observed between remote dimming speed and productivity.  Further, no subject seemed to notice or complain about the dimming speed changes.  


Study Limitations

Reservations effecting of this research include:

1.      In the second phase of this study, 10% of the subject’s salary became based on productivity; although this applied to both the experimental and control subjects, it may have influenced their “standard working hour” values. 

2.      Acknowledgement by the authors that not all factors that may have an influence on productivity could be controlled in a field study.



Article Title: The influence of controllable task-lighting on productivity: a field study in a factory


Publication: Applied Ergonomics 38: 39-44, 2007


Authors: H Juslén, M Wouters, and A Tenner

This article originally appeared in The Ergonomics Report™ on 2007-08-02.