Journal of Health and Safety at Work

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Introduction: According to the literature, a large number of people working in industries and service providing personnel, such as firefighters, physicians, and nurses, are shift workers. The spread of shift working in industrial societies and the incidence of the problems resulting from shift working have caused the researchers to conduct studies on this issue. The present study also aimed to investigate melatonin and cortisol circadian rhythms in the security guards of Shiraz University of Medical Sciences, Shiraz, Iran.

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Material and Method: The present study was conducted among 20 security guards of Shiraz University of Medical Sciences. In order to collect the required data, blood samples were taken from the participants in different times of the day (1, 4, 7, 10, 13, 16, 19, and 22) and cortisol and melatonin levels were determined using radioimmunoassay and enzyme immunoassay techniques, respectively. Then, the data were entered into the SPSS statistical software (v. 16.0) and analyzed using One-Way ANOVA.

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Result: The results showed that as the intensity of light increased during night time, the level of plasma cortisol increased, as well. Besides, no statistically significant difference was found between the plasma cortisol levels in natural light and 4500-lux light. On the other hand, a significant difference was observed between the level of plasma cortisol in natural light and 9000-lux light as well as 4500- and 9000-lux lights. The study findings also showed that as the intensity of light increased at night, the level of plasma melatonin decreased. In addition, a statistically significant difference was found between the plasma melatonin levels in natural light and 4500-lux light. Nevertheless, no significant difference was observed between the plasma melatonin levels in natural light and 9000-lux light as well as 4500- and 9000-lux lights.

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Conclusion: The present study aimed to investigate the subsequences of shift working in the security guards of Shiraz University of Medical Sciences and showed that occupational exposure to bright light could affect some biological markers, such as melatonin and cortisol secretion.

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Introduction: Control room is one of the most important working environments that require optimal performance of individuals to minimize errors. Lighting is one of the environmental factors affecting the operation of the control room operators. Providing optimal lighting in the control room is very important. The purpose of this study was to determine the effect of light on workload, sleepiness, eye fatigue, and satisfaction of individuals from light conditions.

Material and Method: This was an interventional study conducted in a control room of a power plant. Intervention in the control room lighting was performed with two lighting systems including fluorescent lamps (4000 Kelvin, 200 lux) and LED lamps (4,000 Kelvin, 400 lux). Sixteen operators were evaluated under the two lighting systems in terms of workload, sleepiness, eye fatigue and satisfaction of individuals from light conditions.

Result: According to the results, eye fatigue significantly decreased after intervention (p (0.004>. Also, the higher light intensity, significantly decreased the level of sleepiness (p <0.001). In the study of workload, the amount of mental workload (p <0.001) and effort (p <0.03) decreased significantly, after intervention and the increase in the intensity of light; but physical demand, temporal demand, performance and frustration had no significant difference with the results before intervention.

Conclusion: In general, a combination of fluorescent and LED lighting systems, with 400 lux intensity, can provide optimal functional and mental conditions for control room operators. The illumination intensity of 400 lux in terms of workload, sleepiness, eye fatigue and the degree of satisfaction of individuals from light conditions provides a much better environmental condition than 200 lux.

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Introduction: Recent evidence indicates that lighting can affect physiological and neurobehavioral human functions, referred to as non-image forming (NIF) effects of lighteffects. This study aimed to determine the effects of illumination levels and correlated color temperature (CCT) on alertness and performance under NIF conditions.
Material and Methods: In this study, 22 participants were exposed to light at various levels of illumination, including very low illuminance (<5 lux, control) and light conditions with correlated color temperatures (CCT) of 4000 K, 8000 K, and 12000 K at 300 and 500 lux. The data collection process included recording the power of brainwaves (alpha, alpha-theta, beta, and theta), sleepiness and mood scales, and cognitive performance tests for sustained attention, psychomotor vigilance task (PVT), working memory, and inhibitory capacity.
Results: The results indicated that 500 lux light conditions at correlated color temperatures of 8000 and 12000K significantly reduced normalized alpha, alpha-theta power, subjective sleepiness, and performance compared to the dim light condition. Under illumination levels of 300 and 500 lux, there were no significant differences in the measured values of the variables.
Conclusion: Lighting interventions can be used as a supplement to other strategies for increasing alertness and performance in the workplace.