Stress Research Institute
Promoting alertness and sleep by dynamic lights for control room operators
Arne Lowden, Stress Research Institute, Stockholm University, Sweden
Conclusion
It seems that appropriate dynamic light in windowless rooms during the dark Nordic season
may promote alertness, sleep and better adaptation to quickly rotating shiftwork.
Aim
To improve alertness, sleep and adaptation to rotating shiftwork, a new dynamic light regiment
adjusted to current work hours was tested during the Scandinavian winter.
Methods
The illumination level in a control room at a nuclear power station was about 200 lux at the work
stations (horizontal gaze). New lights were installed in part of the control room, see figure 1.
Three levels of exposure were used, see figure 2. Operators were followed with sleep/wake diaries during one week (starting on Saturday) in the shift sequence NNNxMMA (N=night, x=day
off, M=morning, A=afternoon). They were studied in a crossover design with 7 weeks in-between
study weeks. The study was conducted during winter months with no opportunities to receive
day light exposure after night work or before morning work. Operators were given actigraphs,
filled in a sleep/wake diary and melatonin saliva samples were collected at work (only ratings
presented here). Ratings of KSS (Karolinska Sleepiness Scale) were given every second hour. ANOVAs were calculated in connection to night work, free days and morning work using the factors
group (exposed reactor operators/non-exposed controls) (new/old exposure) and time.
Study groups
7 reactor operators (experimental group, mean age 50.2 yrs) and 15 turbine operators/technicians (control group, mean age 46 yrs) from seven different teams participated.
Results
Results from the wake/sleep diary showed that the new light treatment decreased sleepiness in
connection to night work, in particular during the second night shift, see figure 3 (interaction
group x light x time, p<0.05). During free days after night work, sleep length increased with 0.7
hours to 7.42 hours with the new lights (interaction group x light, p<0.05) and these days were
rated as being better (interaction group x light, p<0.05). Sleepiness in connection to the first
morning shift did not differ in-between conditions or groups, see figure 4.
Figure 1. New fixtures (Savio) and old lighting above operators.
1
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Strong blue/white
Moderate yellow
Weak yellow
Mon
N3
1:st morning shift
2:nd night
g
shift
d
Strong blue/white
Moderate yellow
Weak yellow
Tue
d
Strong blue/white
Moderate yellow
Weak yellow
7
7
6
6
Thu
M2
Strong
Strong blue/white
blue/white
Moderate
Moderate yellow
yellow
Weak
yellow
Weak yellow
Strong blue/white
Moderate yellow
Weak yellow
8
Wed
M1
Strong blue/white
d
Moderate yellow
Weak yellow
Strong blue/white
Moderate yellow
Weak yellow
8
A1
N1
N2
Fri
Sat
Sun
Figure 2. Light schedule. Three levels of exposure gave either a white strong light (1050lux,
6000K) a yellow moderate light (700lux, 4000K) or a yellow light (650lux, 3000K).
Stress Research Institute is a knowledge centre in the area of stress and health. The Institute is part of
the Faculty of Social Science, Stockholm University, Sweden and conducts basic and applied research on
multidisciplinary and interdisciplinary methodological approaches.
E-mail [email protected]
Website www.stressresearch.se
Control light
Control_light
KSS
5
Control_dark
Experimental_light
4
Experimental_dark
Control_light
KSS
5
Experimental_light
4
3
3
2
2
14 16 18 20 22 24 2
4
6
8
Time
Figure 3. Sleepiness ratings (KSS) given in connection to the second night shift.
Control_dark
l d k
Experimental dark
Experimental_dark
5
6
8 10 12 14 16 18 20 22 24
Time
Figure 4. Sleepiness ratings (KSS) given in connection to the first morning shift.
CONTACT
Arne Lowden, Stress Research Institute, Stockholm University
E-mail [email protected]
Phone +46 8 5537 8915