Effect of Insufficient Environmental Brightness on Musculoskeletal System of Human Care Workers

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The effect of brightness on work style was studied to assess the working conditions of human care workers who often work under insufficient brightness in night.1. To record the relative position of a subject in a work place, a software that controls the electromagnetic position measuring apparatus was developed.2. Using the developed system, a baggage handling work was measured at the environmental brightness of 1, 10, 40 and 150 Lx. Ten subjects brought 8 boxes between the low and high tables for three times. Total work time was increased in the darker condition. The postural variation indicated by the standard deviation of the trunk inclination was also increased. The subjective complaint of difficulty for working was remarkable at 1 Lx. The effect of brightness was clear in mental stress, not in physical stress.3. The effect of environmental brightness on a model work of human care was studied at 1, 10, 40 and 400 Lx. Four subjects attended the experiment as both workers and patients. The worker transferred the patient from the bed to wheelchair by manual. It consists of three steps; (1) preparation step to make the patient to sit on the bed, (2) transfer step, and (3) settlement step to set the feet of the patient on the foot steps of wheelchair. The workers tended to keep more distance from the bed at the preparation step in the darker condition. At the settlement step, workers tended to keep their face near to the foot steps. No positional and postural differences were observed at the transfer step. The subjective complaint of increase in mental stress and uncertainty of footstep was clear when working darker condition.