Assessment of blue light exposure in the occupational visual field
Date
2020
Authors
Lee, So Young
Editors
Advisors
Pisaniello, Dino
Gaskin, Sharyn
Piccoli, Bruno
Gaskin, Sharyn
Piccoli, Bruno
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Thesis
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Abstract
Problem statement: Rapid technological advances are occurring in the lighting industry, with greater diffusion of cost-effective sources incorporating light emitting diode (LED) and metal halide lamps. These new lamps are often brighter than traditional lamps and are widely used in various applications from general homes to medical/industrial settings. They can have significantly different spectral radiant energy distributions, including shorter wavelengths. Intense blue-rich lamps may represent a hazard, i.e. the so-called “blue light” hazard, and potentially contribute to age-related macular degeneration (AMD). The mechanism of retinal damage is believed to be associated with photochemical oxidation, leading to cumulative loss of photoreceptors. From a public health perspective, AMD is the major cause of low vision and blindness in older people aged 50 and over. As blue light-related AMD, like noise-related hearing loss, can be progressive, there may not be any obvious symptoms. Given the increasingly wide distribution of blue-rich light sources there is a need to better understand blue light exposure, and how these exposures are linked to macular degeneration. Gap analysis: The existing literature related to blue light exposure and potential health effects are scattered in multidisciplinary areas, such as medicine, physics, occupational hygiene, biology, chemistry, and nutrition. There is a shortage of literature from an occupational health perspective. Hence, there is a need to organise the evidence and interpret the literature for occupational health professionals, who advise management and workers on workplace hazards. It is also clear that exposure studies of workers using blue light sources are limited, potentially due to the complexity/cost of measurement. Exposure assessment is a complex task requiring detailed time/activity assessment relative to direct and reflected blue light in the visual field. Purpose statement: This exploratory research has two aims. Firstly, it aims to gather evidence about blue light exposures and risks of retinal photochemical damage through reviewing available published literature. Secondly, it aims to conduct empirical case studies for selected work environments and tasks and compare measured values with current exposure guidelines. General Research questions: 1. How significant is blue light exposure in the Occupational Visual Field (OVF)? a. What evidence is there relating to occupational blue light hazards/exposures/controls? (Literature review) b. Is the exposure of selected workers in proximity to known blue light sources sufficient to exceed the current blue light exposure TLVs? (Case study approach) Methodology: The methodology comprises comprise a narrative literature review and three empirical case studies. Literature Review: The literature review was conducted in terms of an occupational hygiene paradigm (Hazard/Exposure/Control) with a systematic search strategy using PubMed, Scopus and Embase databases and hand-searching. The review covered the areas of the recognition of blue light hazards, measuring the exposure, and recommending how to control the exposure and hazards. The results of the search were tabulated and summarized to assess the quality of evidence. The yield was classified into 3 levels of quality (High, Medium, and Low). JBI and SYRCLE tools were used for the classification. The audience for the review is occupational health professionals, regulators and industrial unions. Three Case studies in different workplaces with blue light sources: All case studies were approached in the same way. Firstly, field observations were conducted to understand; the workers’ task, working processes, durations and estimated observation distances and average frequency of light exposure. Secondly, using the observational data, blue light exposure in a nail salon, video recording studio and dental simulation clinic using blue light sources were simulated and a comparison made with existing exposure guidelines. • Case study 1 (Nail curing lamp) Observations in seven nail salons in Adelaide were conducted to observe the tasks, work durations, types of light sources and other working conditions. Nail art videos on the internet were also watched to characterise the diversity of nail technicians’ working processes. The information obtained from field observations in a series of salons was used in conjunction with a series of laboratory experiments that simulated exposure using two nail curing lamps. • Case study 2 (Various light sources in a video recording studio) Observational data in a video recording studio in the University of Adelaide were collected with the three most common lighting backgrounds (panel LEDs, spotlights and ceiling lamps). Three probable recording scenarios were created from the observations and each light source was directly measured in the user’s OVFs using three scenarios in the studio. • Case study 3 (dental curing lamp) Observations in the dental simulation clinic in the University of Adelaide were conducted to understand simulation courses using a dental curing lamp, curing durations, types of light sources in the clinic and other students’ working conditions. Assessments of a dental curing lamp were conducted in both the simulation clinic and in a laboratory. A spectroradiometer (Specbos 1211UV) was used to measure the spectral radiances in the OVF. The data were compared to the exposure guidelines e.g. American Conference of Governmental Industrial Hygienists Threshold Limit Values (ACGIH TLV) and International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. Blue light hazard function (BLHF) illuminance To measure BLHF illuminance and irradiance, a blue filter (HOYA B440) was used on a professional lux meter (as above) and with the mobile devices. Blue light hazard function (BLHF) luminance To measure BLHF luminance, a blue filter (HOYA B440) was used on a professional luminance meter (Minolta nt-1°). Main Findings Narrative literature review (OVF perspective) Hazard - Blue light exposure can damage the visual photoreceptors and lead to degenerative retinal diseases. The damage from sources can be cumulative and irreversible. Workers who are exposed to very intense sources, such as arc welding lamps, can be more at risk of retinal damage than other workers. A wider group of workers with chronic exposures to sources such as blue rich LEDs may experience long term effects. Generally aging is closely related to retinal photochemical injuries. Younger eyes (less than 20 years old) exposed to blue light have been reported to have a 20 % increased risk for retinal photochemical damage compared to the eyes in people in their 60s. Therefore, it is possible that workers who are exposed to blue light sources for a long time may have the potential risk of retinal damage. AMD, one of the most common retinal diseases, mainly occurs in elderly populations. It can be caused by many potential risk factors and occupational long term blue light (380- 550 nm) exposure could be one of those. It should be noted that new approaches for treating retinal damage, such as retinal stem cells or nutritional supplements, have been recently described. Exposure - It is difficult to estimate the potential risk on eyes from blue light exposure. The OVF should be considered in the workplace due to eye/head movements, the actual task and worker’s behaviour. ICNIRP guidelines consider the field of view from blue light exposure utilising a range of acceptance averaging angles depending on exposure duration. The blue light effective radiance (LB) and the radiance dose (DB) are defined as exposure parameters, and guidelines stem from animal studies and acute exposures. Controls - The hazard control literature largely relates to personal protective equipment, selection and management of sources. Case study 1 (nail curing lamp: UV nail curing lamps which are designed for nail coating curing processes, emit UV radiation (UVR) and blue light. There are two types of UV nail lamps (UV fluorescent and LED lamps) and LED type curing lamps are the most common type of the lamps used currently. Two LED lamps were considered in lab simulation. The highest peak emission of both LED nail lamps was at 404 nm. The stronger powered (36W) LED nail lamp showed higher radiances than the low powered (18W) lamp. The levels of radiance and radiance dose (LBs and DBs) were well below the current limits, even in the worst case exposure scenario. The design of UV nail lamp openings is such that they generally face the actual users and thus customers may have higher exposures than nail technicians during the brief curing process. However, most customers only visit nail salons periodically (e.g. monthly), while nail technicians have many customers to attend to daily. Hence, the duration of workers’ exposure to UV nail lamps would greatly exceed that of a typical customer’s exposure (e.g. Estimated viewing durations in worst case were 900 seconds for a customer and 2700 seconds for a nail technician.) Interestingly, the corners of the 18W LED nail curing lamp showed higher values of LBs than at the centre. This indicates that the amount of exposure can differ depending on the position of the person. This research is the first to attempt to measure the spectral radiances and the spectral radiance doses in terms of the actual working environment. Case study 2 (bright light sources in a video recording studio): Several standard presentation options were available. Depending on the options selected different light sources are introduced (e.g. spotlight, vs soft lights and side lights). Generally, the lights in a video recording studio are brighter than in typical offices or industrial areas. Except for the spotlight option, all light sources in the studio were installed to the ceiling and toward the centre of the stage and did not face toward a presenter’s eyes directly when the presenter looks to the front. However, the eyes and the head of a human being move continuously and a presenter/presenters can have diverse working positions during recording. Especially, when two presenters are sitting across from each other under front light sources, both people can be exposed to intense bright light sources. The radiance of spotlights exceeds 100 W/m2sr and the contrast between the illuminated spot and dark background studio was very high and discomfort glare is indicated. Depending on the motion of a presenter, one or more front light sources (4 LED panels and 2 spotlight LEDs) were included in the OVF. Generally, blue weighted radiance levels did not exceed the limit, and radiance doses are not expected to be exceeded under normal usage. Case study 3 (dental curing lamp): A dental curing lamp emits blue light wavelengths ranging from 400 to 450 nm and is used for polymerizing dental resin-based materials. Dental students using a dental simulation suite were observed. Second year dental students receive their practical training in the dental simulation clinic for around 160 hours per one semester. The working distances were quite close from 15 to 30 cm and the average of angles from the teeth-treated to students’ eyes was 45 degrees. However, both distances and angles varied depending on the locations of the treatment. The potential exposure duration of a typical- and the worst-case scenario estimated by the observations were 108 sec and 240 sec during 3-hour classes respectively. The blue weighted radiance levels were highly variable depending on targets, angles and the locations of teeth, ranging from 2.5 to 212 W/m2sr. Novelty: This research is novel in terms of systematically assessing blue light exposure in the occupational visual field, both in terms of radiance and radiance dose. The exposure to blue light sources was characterised by a combination of radiance measurement and time activity patterns through the data from actual fieldwork observations. Lastly, preliminary research into how low-cost photometry (illuminance and luminance) could be adapted for radiometry was undertaken. Conclusions: Blue light exposures in the three case studies were generally low. However, exposure is highly directional. Intense blue rich sources in the occupational visual field may pose appreciable retinal risks. Blue light exposures with hand held sources are problematic. With few empirical studies, multidisciplinary literature, and expensive instrumentation it appears that most occupational health professionals are unfamiliar with the blue light exposure assessment technology. Recommendations: Based on the research conducted, several recommendations can be made for researchers, occupational health professionals and manufacturers. For researchers: Systematic exposure assessment and epidemiological studies are needed. These will assist in formulating human-derived exposure standards. For occupational health professionals: Occupational health professionals should understand light sources through lighting surveys in the workplace and should assess the blue light exposure in the OVF taking into account time activity patterns and directionality of lighting. For manufacturers: More specific information related to classifications of their light sources and potential health effects from exposure should be provided for users. The design of lighting systems may influence exposure. In terms of managing potential exposure in a nail salon context, a covered design is recommended. A modified dental curing lamp with a separate annular light source could be developed for users wearing blue filtering glasses. This would assist in more precise curing, whilst also protecting the dentist.
School/Discipline
School of Public Health
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Public Health, 2020
Provenance
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