Bright-light therapy may reduce attention lapses during night work

By Tarun Sai LomteReviewed by Susha Cheriyedath, M.Sc.Aug 11 2026

A meta-analysis suggests bright-light exposure can sharpen alertness and attention during simulated night work, but researchers say the optimal dose, timing, and real-world benefits remain uncertain.

Study: Shining a light on cognitive performance: A systematic review and meta-analysis on light therapy on simulated night shifts. Image Credit: ultramansk / Shutterstock

In a recent study accepted for publication in the journal Scientific Reports, researchers evaluated the impact of light therapy on cognitive performance under simulated night-shift conditions.

Shift work is a non-standard work schedule involving evening or night shifts, long working hours, and on-call shifts, and it has long-term health consequences. Sleep-related disorders and impaired cognitive performance are among the most common immediate consequences of shift work. Light therapy aims to improve adaptation to night shifts, phase-shift circadian rhythms, and enhance sleep outcomes and cognitive performance. Despite decades of research, there is no consensus on the efficacy of light therapy for improving cognitive performance.

About the study

In the present study, researchers assessed the effects of light therapy on cognitive performance under simulated night-shift conditions. A systematic literature search was conducted in Embase, PubMed, Cochrane Library, PsycINFO, and Web of Science for studies that measured cognitive performance during or after light therapy relative to a control condition in simulated night shifts.

Eligible studies had a controlled design, used light therapy at a level of at least 1,000 lux for any duration, and included healthy, working-age adults aged 18–65 years. Relevant data, including study details, participant characteristics, intervention details, and outcome measures, were extracted from the included studies. The Scottish Intercollegiate Guidelines Network (SIGN) checklists and Joanna Briggs Institute (JBI) criteria were used to assess the methodological quality of studies.

Multi-level meta-analyses were performed using a restricted maximum likelihood approach; specifically, analyses compared cognitive performance between the intervention and control groups at baseline (t0), in the intervention group during (t1) and after (t2) light therapy relative to t0, and in the control group at t1 and t2 relative to t0. Changes in the intervention group at t1 and t2 relative to t0 were also compared to those in the control group.

Results were stratified by cognitive performance measure type. In addition, sensitivity analyses were conducted by excluding outliers, by including only randomized controlled trials (RCTs), and by using conventional random-effects meta-analysis (i.e., the DerSimonian–Laird approach). Meta-regressions were performed to assess whether individual or intervention characteristics influenced the effects of light therapy.

Findings

The literature search yielded 2,917 records, of which 16 studies with 311 participants were included in the meta-analysis. Six studies were RCTs, and 10 were quasi-experimental studies. Mean quality scores were 61.5% and 70% for RCTs, and 90.9% and 72.7% for non-RCTs based on JBI and SIGN criteria, respectively. The certainty of evidence was moderate for the main outcome and low for most secondary outcomes. All studies objectively assessed cognitive performance. However, most studies (61%) also evaluated subjective measures.

Participants were predominantly young and male, with a mean age of about 24 years and 78% being male, potentially limiting the applicability of the findings to the broader shift-working population. Cognitive performance measures included alertness in 13 studies, attention/reaction time in eight studies, and executive function in 11 studies. Outcomes were measured at t1 in all studies except one.

The intensity of light therapy ranged from 1,056 lux to 10,000 lux across studies, while controls were exposed to dim light ranging from 5 lux to 316 lux. Bright-light exposure ranged from 45 minutes to 14 hours, with an average of 5.95 hours, and control participants were exposed to dim light for the same duration.

At t0, there were no differences in the overall cognitive performance between the intervention and control groups. At t1, the light-therapy group showed better overall cognitive performance than the control group, both after outlier exclusion and in the conventional meta-analysis. Moreover, alertness improved only with light therapy in RCTs. Executive function improved with light therapy in multi-level and conventional meta-analyses and after outlier exclusion.

At t2, only conventional meta-analysis revealed better overall cognitive performance in the light-therapy group. Alertness and attention/reaction time improved with light therapy in multi-level and conventional meta-analyses, in RCTs only, and after outlier exclusion. Attention/reaction time also improved in an analysis restricted to studies using the psychomotor vigilance test. The overall cognitive performance improvement from t0 to t1 was greater with light therapy than with control conditions in multi-level and conventional analyses, in RCTs only, and after outlier exclusion.

The change in overall cognitive performance from t0 to t2 favored light therapy in the conventional meta-analysis and after outlier exclusion. Alertness improved between t1 and t0 with light therapy in the multi-level meta-analysis after outlier exclusion, and only in RCTs. Between t2 and t0, alertness also improved across these analyses and in the conventional meta-analysis.

Attention/reaction time improved from t0 to t2 with light therapy in multi-level and conventional meta-analyses and after outlier exclusion. Executive function improved from t0 to t1 but declined from t0 to t2 in the multi-level analysis and after outlier exclusion. The authors placed greater emphasis on these changes from baseline because they more directly reflected treatment effects and were less susceptible to potential baseline differences between the groups.

Meta-regressions indicated that greater cumulative light exposure before assessment at t1 and t2 was associated with reduced benefits of light therapy. An exploratory analysis also suggested a possible inverted U-shaped relationship between cumulative light exposure and cognitive performance, but the authors cautioned that this finding was hypothesis-generating rather than a clinical exposure threshold.

The findings should also be interpreted cautiously because of substantial heterogeneity, small sample sizes, and the predominance of non-randomized studies. Some protocols lacked follow-up or did not reflect real-world night-shift conditions, while the predominance of young participants further limits generalizability to actual shift workers.

Conclusions

In summary, the findings suggest potential benefits of light therapy on cognitive performance despite methodological limitations and heterogeneity. The greatest effects were observed for attention/reaction time and alertness after light therapy, with only smaller effects on executive function limited to the treatment period. Further research is required to elucidate the underlying mechanisms and determine the optimal intensity, timing, duration, and cumulative dose of light exposure.