A British crossover study involving 94 white collar workers associated blue-enriched white fluorescent tube lighting with increased employee daytime alertness, improved employee performance, better mood and less eye strain as compared to regular white fluorescent tube office lighting.
Through a series of subjective employee questionnaires, the research also revealed that blue-enriched white lighting increased night-time sleep quality and longer night-time sleep duration.
The Bottom Line – How This Applies To Ergonomists
Blue-enriched white light may be an affective engineering control to lessen multiple physical and psychosocial risk factors.
Further, this study supports the opinion of some employees that traditional white office fluorescent lighting is irritating/suboptimal. Investigators have found a melanopsin-dependent photoreceptive system in the retinal ganglion cells of the eye which is activated by 480 nm wavelengths – blue light. This system may explain the study findings.
Ninety-four white collar workers participated – 45 females, 49 males.
This study was conducted from January to March on the third and fourth floors (the two floors had a similar lay-out) of a large office building. The subjects’ work shift generally started at 8:30 am and ended at 4:45 pm (at the beginning of the study, sunrise occurred at 7:55 am while at the end occurred at 6:09 am: sunset ranged from 4:36 pm to 6:13 pm).
The Lighting Exposure
Highly correlated color temperature (17,000 K, Philips master TL-D Activiva) and lower color temperature (4000 K, Philips master Tl-D super 80) fluorescent tubes were used. The 17000 K tube produced the blue-enriched white light by having more 420 to 480 nm output. The mean illuminance levels at the work surfaces were 310.35 lx for the blue-enriched white light and 421.07 lx for the white light.
Baseline assessments were conducted while the subjects were exposed to their normal lighting in the week prior to the beginning of the experiment. The lighting change occurred over a weekend. On one floor, the subjects performed work while exposed to blue-enriched white light for four weeks followed by exposure to white light for four weeks. On the other floor, the subjects were first exposed to white light for four weeks followed by four weeks of blue-enriched white light. The crossover study design allowed for an evaluation of the exposure and the floor.
At baseline, the following assessments were completed by the subjects.
• General demographics information
• Pittsburgh Sleep Quality Index
• Horne-Östberg Questionnaire for diurnal preference
• Seven point Likert scale for the evaluation of vitality, energy, activity, alertness, concentration, tiredness, and trouble thinking over the prior three-day period
• Nine point Likert scale for the evaluation of daytime alertness, performance, and evening fatigue changed over a two week period
During the two four-week exposure trials, the participants completed assessments on each Tuesday.
During the morning, they completed:
• Karolinska Sleep Diary (KSD)
• Morning Need of Recovery Scale, modified
• Karolinska Sleepiness Scale (KSS)
• Rating Scale Mental Effort (RSME)
At noon, subjects repeated the KSS and RSME questionnaires.
In the late afternoon, the following evaluations were completed:
• The Headache and Eye Strain Scale (H&ES)
• Positive and Negative Affect Scale (PANAS)
To assess the subjects’ expectations of a lighting alteration, the seven point Likert scale questionnaire was given on the first days following a lighting change. Also, a five point Likert scale questionnaire was given to disclose how employees felt about the change in lighting.
1) The “Expectation Questionnaire” revealed that the volunteers had no particular anticipation of the impact of white or blue-enriched lighting impact.
2) The study subjects were blinded relative to researcher expectations from lighting changes but they were not blind to the actual changes in the lighting.
3) The crossover design eliminated the possibility of an order effect or seasonal effect.
Article Title: Blue-enriched white light in the workplace improves self-reported alertness, performance and sleep quality
Publication: Scandinavian Journal of Work, Environment & Health, 34(4), 297-306, 2008
Authors: A U Viola, L M James, L J Schlangen, D-J Dijk
This article originally appeared in The Ergonomics Report™ on 2008-12-17.