Viola 2008.

Methods	Controlled before‐after study with cluster allocation and cross‐over design. Comparison: high CCT vs standard illumination.
Participants	94 white‐collar workers, working at a distribution company in northern England, at latitude of 52º north. Two floors of a large office building, which housed the company, were selected and used. Each floor was the same with regard to layout of desks and environmental light exposure. The two floors were also very similar with respect to nature of work carried out. The habitual start was 08:30 a.m. and end time was 16:45 p.m. of work on both floors. First floor: 52 participants (26 women, aged: mean ± SD: 34.6 ± 1.4 years). Second floor: 42 participants (19 women, aged mean ± SD: 37.4 ± 1.5 years).
Interventions	Two periods of four weeks under different light conditions (17,000 and 4000 K). Intervention 1: newly developed fluorescent light source with a highly CCT (17,000 K, Philip Master TL‐D ActiViva Active, Philips, Roozendaal, the Netherlands). Intervention 2: similar light source with a lower CCT (4000 K, Philips Master TL‐D super 80). Both types of fluorescent tubes were 18 W and had a similar spectral power distribution in the medium and long wavelength ranges, but the 17,000 K light source produced more output between 420 nm and 480 nm.
Outcomes	Alertness assessed by Karolinska Sleepiness Scale. Questionnaires were completed on a weekly basis. Positive and negative mood assessed by PANAS scale. Adverse events (irritability, headache, eye strain, eyes discomfort, eye fatigue, difficult focusing, difficult concentrating and blurred vision) assessed by questionnaire. Symptoms were rated from 1 to 4 (severe). Outcomes reported as means of all measurements performed in different time points.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Comment: non‐randomised study.
Allocation concealment (selection bias)	High risk	Comment: non‐randomised study.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Comment: different lighting conditions.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Quote: "During the two 4‐week periods of exposure to experimental lighting conditions, the participants completed questionnaires in the morning, midday, and late afternoon on the Tuesday of every week. They were requested to complete the morning measures in the hour after their arrival at work and to consider only the time since their arrival at work." Comments: self‐assessment questionnaires. Participants were not blind to interventions.
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: "Ten participants withdrew from the study. The reasons for withdrawal included loss of interest in the study, change of floor during the study, and time off work during the study. The analyses presented in this report are therefore based on 94 participants." Comments: attrition rate 10.6%. Reasons justifying withdrawal included loss of interest in study, change of floor during study and time off during study. Withdrawals in each group were not reported.
Selective reporting (reporting bias)	Low risk	Comment: data reported for all outcomes.
Other bias	Low risk	Comment: no other bias identified.
Recruitment bias	Unclear risk	Comment: rate of acceptance of participation not reported.
Baseline imbalance	Low risk	Comment: cross‐over design
Loss of clusters	Low risk	Comment: no loss of clusters.
Incorrect analysis	High risk	Comment: unit of allocation (cluster) not taken into account in statistical analysis.
Comparability with individually randomised trials	Unclear risk	Comment: no individually randomised trial focusing on the same type of intervention was identified.
Carry‐over effect	Unclear risk	Comments: no washout period. Carry‐over effect influencing mood could not be disregarded.
Availability of 2‐period data	Low risk	Comment: data from both periods presented.
Incorrect analysis	Low risk	Comment: comparisons of repeated measures were made between the light condition using mixed‐models analyses of variance for repeated measures.
Comparability of results with those from parallel‐group trials	Low risk	Comment: results were in accordance with those from parallel‐group trials (Mills 2007).

CCT: correlated colour temperature; CI: confidence interval; HDRS‐17: 17‐item Hamilton Depressive Rating Scale; HDRS‐21: 21‐item Hamilton Depressive Rating Scale; LED: light‐emitting diode; n: number of participants; PANAS: Positive and Negative Affect Schedule; SAD: seasonal affective disorder; SD: standard deviation; SIGH‐HDRS: Structured Interview Guide for the Hamilton Depressive Rating Scale; SIGH‐SAD: Structured Interview Guide for the Hamilton Depression Rating Scale‐Seasonal Affective Disorders Version; SMD: standardised mean difference; VAS: visual analogue scale.