Combined effect of noise and illumination on worker performance A. K. Gorai, a) T. J. Siddiqui, b) U. K. Dey c) and Gurdeep Singh d) (Received 2006 November 06; revised 2007 May 25; accepted 2007 May 29) This paper elucidates the effect of environmental stressors, viz. noise and illumination, on operator’s performance.The effect of environmental stressor on the performance of tasks is studied in a workshop where work situations are simulated. The study was conducted on two machines, namely a lathe and a shaper, to explore the individual as well as combined effect of noise and illumination levels on operator’s performance. The performance was found to decrease slowly as either the illumination level or noise level increased while keeping the other one fixed. But the performance level decreased more rapidly as both the noise and illumination level were increased simultaneously. The relationship between the equivalent noise level or illumination level and workers performance was found to be statistically significant as the correlation coefficients of all the relations were high. © 2007 Institute of Noise Control Engineering. Primary subject classification: 63.5; Secondary subject classification: 53.1 1 INTRODUCTION Noise is an unwanted sound which has been defined as “that auditory stimulus or stimuli bearing no infor- mational relationship to the presence or completion of the immediate task” 1 . The ubiquitous presence of noise in industry may cause degradation of the performance of the workers. Furthermore, improper illumination levels could reduce productivity and enhance risk to health and safety of workers. There are a few studies that unequivocally show a relation between noise and productivity. The effect of noise on the performance of tasks has mainly been studied in the laboratory and to some extent in work situations, but, there have been few, if any, detailed studies of the effects of noise on human productivity in community situations 2 . Most of the studies showed negative effects of noise on productivity. On the other hand, productivity has been shown to increase in noisy industrial settings when ear protection devices are worn 3–5 . Again subjects highly sensitive to noise performed significantly poorer in challenging mental processes (i.e. difficult mental arithmetic) as compared to subjects less sensitive to noise 6,7 . Tasks that demand continuous and sustained attention to detail, require attention to multiple cues, and require large working memory capacity are all susceptible to adverse effects of noise. Noise has a persistent and well documented effect on tasks that require attention to dual tasks 5,8 . Specifically, errors occur in the task(s) of secondary importance as defined either by instructions or payoff matrices 9 . Tasks that are secondary in importance are missed and/or responded to more slowly under noisy conditions. The effect is not due to a narrowing of attention as originally thought. The uncontrollability of noise rather than the intensity of the noise appear to be the most critical variable 8 . A large number of researches 10–12 have been conducted in the past on both the noise and illumina- tion in the context of human performance. A laboratory experiment on lightning levels and visual tasks showed that usual performance hardly increased above an illuminance of 100 lux 13 . According to Sanders and McCormic, higher levels of illumination were not acceptable for certain tasks because visual perfor- mance of the subjects deteriorated as the level of illumination increased 14 . The objective of this study is, therefore, to examine whether the combined effects of noise and illumination have a greater effect in human functions than the independent effects of either of these factors. In this paper, the performance effects of lathe and shaper operators in different noise and illumination levels are presented. a) Department of Mining Engineering, B.I.T. Sindri, Dhan- bad, Jharkhand – 828123 INDIA; email: amit_gorai@yahoo.co.uk b) Centre of Mining Environment, I.S.M.U., B.I.T. Sindri, Dhanbad, Jharkhand – 826004 INDIA. c) Department of Mining Engineering, B.I.T. Sindri, Dhan- bad, Jharkhand – 828123 INDIA. d) Centre of Mining Environment, I.S.M.U., Dhanbad, Jhark- hand – 826004 INDIA. Noise Control Eng. J. 55 (4), 2007 July-Aug 417