Investigating the impacts of artificial light via blackouts.

Natural experiments provide remarkable opportunities to test the large-scale effects of human activities. Widespread energy blackouts offer such an 'experiment' to test the impacts of artificial light at night (ALAN) on wildlife. We use the situation in South Africa, where regular scheduled blackouts are being implemented, to highlight this opportunity.

Outdoor artificial light at night exposure and gestational diabetes mellitus: a case-control study.

Objective: This study aims to explore the association between outdoor artificial light at night (ALAN) exposure and gestational diabetes mellitus (GDM). Methods: This study is a retrospective case-control study. According with quantiles, ALAN has been classified into three categories (Q1-Q3). GDM was diagnosed through oral glucose tolerance tests. Conditional logistic regression models were used to evaluate the association between ALAN exposure and GDM risk. The odds ratio (OR) with 95% confidence interval (CI) was used to assess the association. Restricted cubic spline analysis (RCS) was utilized to investigate the no liner association between ALAN and GDM. Results: A total of 5,720 participants were included, comprising 1,430 individuals with GDM and 4,290 matched controls. Pregnant women exposed to higher levels of ALAN during the first trimester exhibited an elevated risk of GDM compared to those with lower exposure levels (Q2 OR = 1.39, 95% CI 1.20-1.63, p < 0.001); (Q3 OR = 1.70, 95% CI 1.44-2.00, p < 0.001). Similarly, elevated ALAN exposure during the second trimester also conferred an increased risk of GDM (second trimester: Q2 OR = 1.70, 95% CI 1.45-1.98, p < 0.001; Q3 OR = 2.08, 95% CI 1.77-2.44, p < 0.001). RCS showed a nonlinear association between ALAN exposure and GDM risk in second trimester pregnancy, with a threshold value of 4.235. Conclusion: Outdoor ALAN exposure during pregnancy is associated with an increased risk of GDM.

When night becomes day: Artificial light at night alters insect behavior under semi-natural conditions.

Light is the most important Zeitgeber for temporal synchronization in nature. Artificial light at night (ALAN) disrupts the natural light-dark rhythmicity and thus negatively affects animal behavior. However, to date, ALAN research has been mostly conducted under laboratory conditions in this context. Here, we used the field cricket, Gryllus bimaculatus, to investigate the effect of ALAN on insect behavior under semi-natural conditions, i.e., under shaded natural lighting conditions, natural temperature and soundscape. Male crickets were placed individually in outdoor enclosures and exposed to ALAN conditions ranging from <0.01 to 1500 lx intensity. The crickets' stridulation behavior was recorded for 14 consecutive days and nights and their daily activity patterns were analysed. ALAN impaired the crickets' stridulation rhythm, evoking a change in the crickets' naturally synchronized daily activity period. This was manifested by a light-intensity-dependent increase in the proportion of insects demonstrating an intrinsic circadian rhythm (free-run behavior). This also resulted in a change in the population's median activity cycle period. These ALAN-induced effects occurred despite the crickets' exposure to almost natural conditions. Our findings provide further validity to our previous studies on ALAN conducted under lab conditions and establish the deleterious impacts of ALAN on animal behavioral patterns. TEASER: Artificial light at night alters cricket behavior and desynchronizes their stridulation even under near-natural conditions.

Outdoor Artificial Light at Night and Reproductive Endocrine and Glucose Homeostasis and Polycystic Ovary Syndrome in Women of Reproductive Age.

BACKGROUND: Artificial light at night, a well-recognized circadian clock disrupter, causes disturbances in endocrine homeostasis. However, the association of artificial light at night with polycystic ovary syndrome (PCOS) is still unknown. This study examines the effects of outdoor artificial light at night on sex hormones, glucose homeostasis markers, and PCOS prevalence in Anhui Province, China. METHODS: We recruited 20,633 women of reproductive age from Anhui Medical University Reproductive Medicine Center. PCOS was diagnosed according to Rotterdam criteria. We estimated long-term (previous year) and short-term (previous month) artificial light at night values for residential addresses using 500 m resolution satellite imagery. We fitted multivariable models, using both linear and logistic regression, to estimate the association of artificial light at night with sex hormones, glucose homeostasis markers, and PCOS prevalence. RESULTS: Both long-term and short-term exposure to outdoor artificial light at night were negatively associated with follicle-stimulating hormone and luteinizing hormone levels, while positively associated with testosterone, fasting insulin, homeostasis model assessment-insulin resistance, and homeostasis model assessment-insulin resistance-ß levels. The second-highest quintile of artificial light at night was associated with increased PCOS prevalence (odds ratio [OR long-term ] = 1.4; 95% confidence interval [CI] = 1.2, 1.6 and OR short-term = 1.3; 95% CI = 1.1, 1.5) compared with the lowest quintile. In addition, prevalence of PCOS was linearly associated with long-term exposure to artificial light at night, but nonlinearly associated with short-term exposure. This association was more evident in younger, obese or overweight, moderately educated, rural women, and for the summer and fall seasons. CONCLUSION: Outdoor artificial light at night may be a novel risk factor for PCOS.

The blue light hazard and its use on the evaluation of photochemical risk for domestic lighting. An in vivo study.

BACKGROUND: Nowadays artificial light highly increases human exposure to light leading to circadian rhythm and sleep perturbations. Moreover, excessive exposure of ocular structures to photons can induce irreversible retinal damage. Meta-analyses showed that sunlight exposure influences the age of onset and the progression of Age-related macular degeneration (AMD), the leading cause of blindness in people over fifty-year old. Currently, the blue-light hazard (BLH) curve is used in the evaluation of the phototoxicity of a light source for domestic lighting regulations. OBJECTIVES: Here, we analyze the phototoxicity threshold in rats and investigate the role played by the light spectrum, assessing the relevance of the use of the BLH-weighting to define phototoxicity. METHODS: We exposed albino rats to increasing doses of blue and white light, or to lights of different colors to evaluate the impact of each component of the white light spectrum on phototoxicity. Cellular mechanisms of cell death and cellular stress induced by light were analyzed. RESULTS: Our results show that the phototoxicity threshold currently accepted for rats is overestimated by a factor of 50 when considering blue light and by a factor of 550 concerning white light. This is the result of the toxicity induced by green light that increases white light toxicity by promoting an inflammatory response. The content of green in white light induces 8 fold more invasion of macrophages in the retina than the content of blue light. Moreover, the use of BLH-weighting does not evaluate the amount of red radiations contained in white light that mitigates damage by inhibiting the nuclear translocation of L-DNase II and reducing by 33% the number of TUNEL-positive cells. DISCUSSION: These findings question the current methods to determine the phototoxicity of a light source and show the necessity to take into account the entire emission spectrum. As current human phototoxicity thresholds were estimated with the same methods used for rats, our results suggest that they might need to be reconsidered.

Nighttime Outdoor Artificial Light and Risk of Age-Related Macular Degeneration.

Importance: Light pollution's impact on human health is increasingly recognized, but its link to exudative age-related macular degeneration (EAMD) remains unclear. Objective: To investigate the association between exposure to outdoor artificial light at night (OALAN) and the risk of incident EAMD. Design, Setting, and Participants: In this nationwide population-based case-control study, all individuals 50 years or older with newly diagnosed EAMD between January 1, 2010, and December 31, 2011, were identified with reference to the Korean National Health Insurance Service registration program database for rare and intractable diseases. Birth year- and sex-matched controls (with no EAMD diagnosis until 2020) were selected at a 1:30 ratio. Data were acquired from May 1 to December 31, 2021, and analyzed from June 1 to November 30, 2022. Exposures: Mean levels of OALAN at participants' residential addresses during 2008 and 2009 were estimated using time-varying satellite data for a composite view of persistent nighttime illumination at an approximate scale of 1 km2. Main Outcomes and Measures: The hazard ratios (HRs) and 95% CIs of the association between residential OALAN and risk of incident EAMD were determined based on maximum likelihood estimation after adjusting for sociodemographic characteristics, comorbidities, and area-level risk factors (ie, nighttime traffic noise and particulate matter of aerodynamic diameter ≤10 µm in each participant's administrative district of residence). Results: A total of 126 418 participants were included in the analysis (mean [SD] age, 66.0 [7.9] years; 78 244 men [61.9%]). Of these, 4078 were patients with newly diagnosed EAMD and 122 340 were EAMD-free matched controls. In fully adjusted models, an IQR (55.8 nW/cm2/sr) increase in OALAN level was associated with an HR of 1.67 (95% CI, 1.56-1.78) for incident EAMD. The exposure-response curve demonstrated a nonlinear, concave upward slope becoming more pronounced at higher levels of light exposure (ie, at approximately 110 nW/cm2/sr). In a subgroup analysis, an IQR increase in OALAN was associated with increased risk of incident EAMD in urban areas (HR, 1.46 [95% CI, 1.33-1.61]) but not in rural areas (HR, 1.01 [95% CI, 0.84-1.22]). Conclusions and Relevance: In this nationwide population-based case-control study, higher levels of residential OALAN were associated with an increased risk of incident EAMD. Future studies with more detailed information on exposure, individual adaptive behaviors, and potential mediators are warranted.

Molecular mechanisms of artificial light at night affecting circadian rhythm disturbance.

Artificial light at night (ALAN) pollution has been regarded as a global environmental concern. More than 80% of the global population is exposed to light pollution. Exacerbating this issue, artificially lit outdoor areas are growing by 2.2% per year, while continuously lit areas have brightened by 2.2% each year due to rapid population growth and expanding urbanization. Furthermore, the increasing prevalence of night shift work and smart device usage contributes to the inescapable influence of ALAN. Studies have shown that ALAN can disrupt endogenous biological clocks, resulting in a disturbance of the circadian rhythm, which ultimately affects various physiological functions. Up until now, scholars have studied various disease mechanisms caused by ALAN that may be related to the response of the circadian system to light. This review outlines the molecular mechanisms by which ALAN causes circadian rhythm abnormalities in sleep disorders, endocrine diseases, cardiovascular disease, cancer, immune impairment, depression, anxiety and cognitive impairments.

Preclinical safety evaluation of continuous UV-A lighting in an operative setting.

BACKGROUND: Germicidal ultraviolet (UV-C) light has been shown as an effective modality for disinfection in laboratory settings and in the operative room. Traditionally, short-wavelength UV-C devices, which have previously been shown to cause DNA damage, are utilized only for disinfection in pre- and post-operative settings and are not continuously active during operations. Continuous use of intraoperative UV light has potential to decrease pathogens and subsequent surgical site infections (SSIs), which arise in approximately 5-15% of operative cases. SSIs are a significant determinant of patient morbidity, readmission rates, and overall cost. Therefore, a method of UV light disinfection with a low risk of DNA damage is needed so that greater antimicrobial protection can be afforded to patients during the entirety of their surgical procedures. A new disinfection device that harnesses longer-wavelength UV-A light to disinfect the surgical field throughout the entirety of the procedure, including pre- and post-operation has been developed. METHODS: This study aimed to determine if UV-A light administered intraoperatively was safe, as defined by the minimal presence of DNA damage and safe amounts of reflection upon medical personnel. Using in vitro models, we examined the differential impacts of UV-C and UV-A light on DNA damage and repair pathways. In a murine model, we looked at the production of DNA damage photoproduction in relation to UV-A versus UV-C exposure. RESULTS: Our results show UV-A light does not induce a significant amount of DNA damage at the cellular or tissue level. Furthermore, a preclinical porcine study showed that surgical personnel were exposed to safe levels of UV-A irradiance from an overhead UV-A light used during an operation. The amount of UV-A transmitted through surgical personal protective equipment (PPE) also remained within safe levels. CONCLUSIONS: In conclusion, we found that UV-A may be safe for intraoperative use.

Light wavelength and pulsing frequency affect avoidance responses of Canada geese.

Collisions between birds and aircraft cause bird mortality, economic damage, and aviation safety hazards. One proposed solution to increasing the distance at which birds detect and move away from an approaching aircraft, ultimately mitigating the probability of collision, is through onboard lighting systems. Lights in vehicles have been shown to lead to earlier reactions in some bird species but they could also generate attraction, potentially increasing the probability of collision. Using information on the visual system of the Canada goose (Branta canadensis), we developed light stimuli of high chromatic contrast to their eyes. We then conducted a controlled behavioral experiment (i.e., single-choice test) to assess the avoidance or attraction responses of Canada geese to LED lights of different wavelengths (blue, 483 nm; red, 631 nm) and pulsing frequencies (steady, pulsing at 2 Hz). Overall, Canada geese tended to avoid the blue light and move towards the red light; however, these responses depended heavily on light exposure order. At the beginning of the experiment, geese tended to avoid the red light. After further exposure the birds developed an attraction to the red light, consistent with the mere exposure effect. The response to the blue light generally followed a U-shape relationship (avoidance, attraction, avoidance) with increasing number of exposures, again consistent with the mere exposure effect, but followed by the satiation effect. Lights pulsing at 2 Hz enhanced avoidance responses under high ambient light conditions; whereas steady lights enhanced avoidance responses under dim ambient light conditions. Our results have implications for the design of lighting systems aimed at mitigating collisions between birds and human objects. LED lights in the blue portion of the spectrum are good candidates for deterrents and lights in the red portion of the spectrum may be counterproductive given the attraction effects with increasing exposure. Additionally, consideration should be given to systems that automatically modify pulsing of the light depending on ambient light intensity to enhance avoidance.

Sleep and circadian disruptors: Unhealthy noise and light levels for hospitalized pediatric patients.

Noise and light levels during hospitalizations can disrupt sleep and circadian health, resulting in worsened health outcomes. This study describes patterns of noise and light for inpatient children undergoing stem cell transplants. Objective meters tracked noise and light levels every minute for 6 months. Median overnight sound was 55 dB (equivalent to conversational speech). There were 3.4 loud noises (>80 dB) per night on average. Children spent 62% of the 24-h cycle in nonoptimal lighting, with daytime light dimmer than recommended 98% of the time. Over the 6-month period, the lowest overnight noise level recorded exceeded World Health Organization recommendations for sleep, with frequent spikes into ranges known to cause wakings. During the day, children were rarely exposed to light sufficient to preserve healthy circadian rhythms. Hospitals should address systematic environmental and workflow disruptors to improve the sleep and circadian health of patients, particularly those already at elevated risk for health morbidities.

Chronodisruption of the acute inflammatory response by night lighting in rats.

Daily oscillations are present in many aspects of the immune system, including responsiveness to infections, allowing temporal alignment of defence mechanisms with the external environment. Our study addresses whether compromised circadian timing function by dim artificial light at night (ALAN) impacts the time dependency of the acute inflammatory response in a rat model of lipopolysaccharide (LPS)-induced inflammation. After 2 weeks of exposure to low-intensity ALAN (~2 lx) or a standard light/dark cycle, male rats were challenged with LPS during either the day or the night. Dim ALAN attenuated the anorectic response when rats were stimulated during their early light phase. Next, ALAN suppressed daily variability in inflammatory changes in blood leukocyte numbers and increased the daytime sensitivity of neutrophils to the priming effects of LPS on oxidative burst. An altered renal inflammatory response in ALAN-exposed rats was manifested by stimulated T-cell infiltration into the kidney upon night-time LPS injection and the modified rhythmic response of genes involved in inflammatory pathways. Moreover, ALAN disturbed steady-state oscillations of the renal molecular clock and eliminated the inflammatory responsiveness of Rev-erbα. Altogether, dim ALAN impaired time-of-day-dependent sensitivity of inflammatory processes, pointing out a causal mechanism between light pollution and negative health effects.

Identifying roadway departure crash patterns on rural two-lane highways under different lighting conditions: Association knowledge using data mining approach.

INTRODUCTION: More than half of all fatalities on U.S. highways occur due to roadway departure (RwD) each year. Previous research has explored various risk factors that contribute to RwD crashes, however, a comprehensive investigation considering the effect of lighting conditions has been insufficiently addressed. DATA: Using the Louisiana Department of Transportation and Development crash database, fatal and injury RwD crashes occurring on rural two-lane (R2L) highways between 2008-2017 were analyzed based on daylight and dark (with and without streetlight). METHOD: This research employed a safe system approach to explore meaningful complex interactions among multidimensional crash risk factors. To accomplish this, an unsupervised data mining algorithm association rules mining (ARM) was utilized. RESULTS AND CONCLUSIONS: Based on the generated rules, the findings reveal several interesting crash patterns in the daylight, dark-with-streetlight, and dark-no-streetlight, emphasizing the importance of investigating RwD crash patterns depending on the lighting conditions. In daylight condition, fatal RwD crashes are associated with cloudy weather conditions, distracted drivers, standing water on the roadway, no seat belt use, and construction zones. In dark lighting condition (with and without streetlight), the majority of the RwD crashes are associated with alcohol/drug involvement, young drivers (15-24 years), driver condition (e.g., inattentive, distracted, illness/fatigued/asleep), and colliding with animal(s). PRACTICAL APPLICATIONS: The findings also reveal how certain driver behavior patterns are connected to RwD crashes, such as a strong association between alcohol/drug intoxication and no seat belt usage in the dark-no-streetlight condition. Based on the identified crash patterns and behavioral characteristics under different lighting conditions, the findings could aid researchers and safety specialists in developing the most effective RwD crash mitigation strategies.

Reducing nighttime light exposure in the urban environment to benefit human health and society.

Nocturnal light pollution can have profound effects on humans and other organisms. Recent research indicates that nighttime outdoor lighting is increasing rapidly. Evidence from controlled laboratory studies demonstrates that nocturnal light exposure can strain the visual system, disrupt circadian physiology, suppress melatonin secretion, and impair sleep. There is a growing body of work pointing to adverse effects of outdoor lighting on human health, including the risk of chronic diseases, but this knowledge is in a more nascent stage. In this Review, we synthesize recent research on the context-specific factors and physiology relevant to nocturnal light exposure in relation to human health and society, identify critical areas for future research, and highlight recent policy steps and recommendations for mitigating light pollution in the urban environment.

Effects of anthropogenic light on species and ecosystems.

Anthropogenic light is ubiquitous in areas where humans are present and is showing a progressive increase worldwide. This has far-reaching consequences for most species and their ecosystems. The effects of anthropogenic light on natural ecosystems are highly variable and complex. Many species suffer from adverse effects and often respond in a highly specific manner. Ostensibly surveyable effects such as attraction and deterrence become complicated because these can depend on the type of behavior and specific locations. Here, we considered how solutions and new technologies could reduce the adverse effects of anthropogenic light. A simple solution to reducing and mitigating the ecological effects of anthropogenic light seems unattainable, because frugal lighting practices and turning off lights may be necessary to eliminate them.

Disaggregating the effects of daytime and nighttime light exposures on obesity, overweight, prostate and breast cancer morbidity worldwide.

Hormone-dependent cancers and overweight/obesity are not necessarily linked but might have similar underlying causes, such as circadian disruption, lack of physical activity, and unhealthy nutrition. Several empirical studies also attribute the rise in these types of morbidity to vitamin D deficiency, linked in turn to insufficient sunlight exposure. Other studies place an emphasis on melatonin (MLT) hormone suppression, associated with artificial light at night (ALAN) exposure. Yet no studies, carried out to date, have attempted to determine which of these environmental risk factors is associated stronger with the morbidity types in question. In this study, we aim to narrow this knowledge gap by analyzing data available for 100+ countries worldwide, while controlling ALAN and solar radiation exposure estimates by several potential confounders, such as GDPpc, GINI inequality index and unhealthy food consumption. As the study reveals, all the morbidity types under analysis are significantly and positively associated with ALAN exposure estimates (p < 0.05), while solar radiation appears to be significantly associated with prostate cancer rates only (p < 0.05), but not with breast cancer or overweight/obesity rates (p > 0.1). To the best of our knowledge, this study is the first that separates the effects of ALAN and daylight exposures on the abovementioned types of morbidity.

The curious case of the Zzz's.

Excessive daytime sleepiness is a common presenting symptom that may present a diagnostic challenge for the sleep medicine clinician. We present a case of an adolescent female with excessive daytime sleepiness and "sleep attacks" who was evaluated using a 2-week sleep log, wrist actigraphy, baseline polysomnogram, and Multiple Sleep Latency Test. Multiple Sleep Latency Test results noted a short mean sleep latency without sleep onset rapid eye movement periods, concerning for possible central disorders of hypersomnolence. However, actigraphy data noted a habitual bedtime of midnight or later, resulting in less than recommended total sleep time for her age on weekdays with extended sleep periods on the weekends. The most unique actigraphy finding was exposure to ambient light throughout most overnight sleep periods. When actigraphy results were discussed with the patient, she revealed recent onset of severe anxiety with fear of sleeping in the dark. This case highlights the importance of thorough clinical evaluation, and careful interpretation of objective tests, when evaluating for causes of excessive daytime sleepiness. CITATION: Dang L, Kanney ML, Hsu DP. The curious case of the Zzz's. J Clin Sleep Med. 2023;19(5):1009-1012.

Retinal risk of endoillumination: A comparison of different ophthalmic illumination systems.

OBJECTIVES: In vitreoretinal surgery, there is always a conflict between bright illumination of the field of operation and retinal safety. This study aimed to investigate different light sources and light guides for their potential retinal risk due to bright illumination. METHODS: Irradiances in the fovea of ex-vivo porcine eyes resulting from different light sources (halogen lamp, xenon lamp and LED) and light guides are investigated for varying distances between the illumination tip and the fovea. The results are examined with regard to their photochemical and thermal retinal hazard and the maximal exposure time. The examination is carried out with the maximum intensity setting of each light source and with normalization to its brightness. MAIN RESULTS: With decreasing distance of the tip of the light source, the retinal hazard increases. The photochemical and thermal retinal hazard at maximum brightness are smallest for the halogen lamp, next for the xenon lamp and highest for the LED. Thus, the exposition time is the longest for the halogen lamp followed by the xenon lamp and the LED. Normalizing the results to the same brightness the maximum exposition time is nearly the same for xenon lamp and LED, but still higher in case of the halogen lamp. CONCLUSIONS: The choice of the most suitable lamp and illumination fiber depends on the intensity and spectral distribution of the illumination system. Concerning brightness, xenon and LED lamp are relatively harmless, but the surgeon should avoid the maximum device intensity.

A flashing light may not be that flashy: A systematic review on critical fusion frequencies.

BACKGROUND: Light pollution could represent one of the main drivers behind the current biodiversity erosion. While the effects of many light components on biodiversity have already been studied, the influence of flicker remains poorly understood. The determination of the threshold frequency at which a flickering light is perceived as continuous by a species, usually called the Critical Fusion Frequency (CFF), could thus help further identify the impacts of artificial lighting on animals. OBJECTIVE: This review aimed at answering the following questions: what is the distribution of CFF between species? Are there differences in how flicker is perceived between taxonomic classes? Which species are more at risk of being impacted by artificial lighting flicker? METHODS: Citations were extracted from three literature databases and were then screened successively on their titles, abstracts and full-texts. Included studies were critically appraised to assess their validity. All relevant data were extracted and analysed to determine the distribution of CFF in the animal kingdom and the influence of experimental designs and species traits on CFF. RESULTS: At first, 4881 citations were found. Screening and critical appraisal provided 200 CFF values for 156 species. Reported values of CFF varied from a maximum of between 300 Hz and 500 Hz for the beetle Melanophila acuminata D. to a mean of 0.57 (± 0.08) Hz for the snail Lissachatina fulica B. Insects and birds had higher CFF than all other studied taxa. Irrespective of taxon, nocturnal species had lower CFF than diurnal and crepuscular ones. CONCLUSIONS: We identified nine crepuscular and nocturnal species that could be impacted by the potential adverse effects of anthropogenic light flicker. We emphasize that there remains a huge gap in our knowledge of flicker perception by animals, which could potentially be hampering our understanding of its impacts on biodiversity, especially in key taxa like bats, nocturnal birds and insects.

Outdoor light at night and risk of liver cancer in the NIH-AARP diet and health study.

PURPOSE: Accumulating evidence suggests that light at night (LAN) disrupts circadian rhythms and may increase risk of liver cancer. However, there is no population-based study that examined LAN and liver cancer risk. Therefore, we aimed to investigate the association between outdoor LAN and liver cancer risk in a prospective cohort. METHODS: Residential outdoor LAN level was measured from satellite imagery in the NIH-AARP Diet and Health Study, a prospective cohort of 451,945 men and women, 50-71 years old. Relative risks (RR) and 95% confidence intervals (CIs) were estimated using Cox proportional hazard models that adjusted for known risk factors for liver cancer and neighborhood characteristics. RESULTS: During an average 12.2 years of follow-up, 897 liver cancers, 603 of which were hepatocellular carcinomas (HCC), were diagnosed. Residential outdoor LAN was not associated with risk of liver cancer (RRQ5 vs Q1 = 0.96, 95% CI: 0.77-1.20, p trend = 0.771) or HCC (RRQ5 vs Q1 = 0.82, 95% CI: 0.62-1.07, p trend = 0.425). CONCLUSION: No association between outdoor LAN and risk of liver cancer or HCC may in part be due to limitations in LAN assessment. More studies on the relationship between light intensity, duration, timing, and wavelength and liver cancer are warranted.