The results of the analysis show that lower lux levels are not good for operators since a higher percentage reported fatigue-related feelings. In addition, higher levels are also associated with causing effects that are related to operator fatigue.
CHAPTER 1 INTRODUCTION
1.1 Aims and Objectives
This dissertation aims to obtain optimum levels for the variables investigated to limit visual fatigue for the process plant operators who work in interaction with Visual Display Units. This study aims to assess the effect of lighting in control rooms by examining how lighting in the visual display units is related to ocular fatigue of the operators. The study will focus on the operators who work in control rooms of process plants with an aim of using a systematic approach to address the increasing cases of fatigue in control rooms. This aim will be complemented by the following objectives which the dissertation aims to achieve
Enhance knowledge and understanding about the effect of lighting on visual fatigue for Process Plant Visual Display Unit (VDU) Operators
Identify and discuss factors that interact with lighting to contribute to fatigue for operators in process plant visual display units
Identify barriers to the state-of-the-art designing of the control rooms
Increase an understanding of the influences that architectural designs can have in the effect of lighting on fatigue
Gain an understanding of the current efforts made in order to improve the designing of the control rooms
Define and describe current state of the control rooms with respect to the design of the VDUs
Improve public awareness about the relationship between lighting in control rooms and fatigue for those who work in them and thereby improve or complement fatigue management and training operations
Recommend interventions designed to decrease the occurrence of fatigue resulting from lighting effects in the VDUs through proposition of fatigue management strategies
Complement existing bodies of research on effect of lighting on ocular fatigue for Process Plant Visual Display Unit operators
1.2 Relevance of the study
The study by the Cardiff Research Program carried out in 2007 assessed fatigue management in the seafarers with an aim of developing best practice proposals that are apposite in addressing problems of fatigue in the ship type and trade. Measurement of fatigue was met with challenges during this study due to lack of standards in the measurement of fatigue- that is to say, there were no standard measures for fatigue. This challenge made it difficult for any meaningful comparisons to be made with an aim of evaluating the results of research studies that had already been carried out.
Nevertheless, the research was a breakthrough into understanding the relationship between lighting and fatigue among seafarers. In other follow ups, researchers from different corners of the globe sought to address the in-depth understanding of the causes of fatigue in control rooms across the board. All this has been done in an attempt to understand the aspect of fatigue as an imperative challenge to performance in control rooms.
Around the world, fatigue is identified as one of the major causes of accidents in plants, control rooms and even among drivers and pilots. For instance, a research study done by the Adelaide Center for Research in Australia found that about 20 of accidents occurring in plants result from fatigue of the operators. Health and safety regulations in Europe require that the visual display units be included with measures that are instituted to reduce the effects of fatigue due to lighting in the rooms.
In the USA, the Pipeline and Hazardous Materials Safety Administration (PHMSA) requires that all control rooms be established with control management systems that reduce risks of operators being exposed to risks of fatigue. Nevertheless, most of the research works carried out has been instituted to assess the effect of fatigue on operator performance and few of them have endeavored to evaluate the relationship between the lighting system in the control rooms and the operator fatigue even though the findings indicate a positive relationship between fatigue and incidences of accidents.
Estimates of the predominance of eye problems related to using visual display terminals (VDTs) differ enormously subject to the sample tested as well as the research methods deployed. However, a majority of scholars and authors consent that eye problems are frequent among VDT users.
This dissertation discusses the relative contributions of the nature of VDT displays, design of control rooms, work-practices and optometric aspects in reference to body of literature that is now availed on this subject.
Operator fatigue is a vital safety concern that is experienced in all modes of plants with control rooms. Fatigue can instigate sleepiness and drowsiness, reduce the ability of workers to work safely, and thereby intensify the probability of fatalities and injuries.
1.3 Ergonomic design principles
Thorough analysis of the tasks undertaken by each operator, general principles of ergonomic design should be used to establish the safest and most proficient methods to make best use of human performance. Operators body postures, ocular comfort and movement must be taken into account for proper ergonomic design of a control console to be achieved.
In addition, environmental factors are also considered and these include noise in the surrounding and illumination levels. If an ergonomic design is properly selected it should aim to ease operator stress and to improve alertness at all times. This will allow the operators to stay focused on their tasks. Control consoles should follow the following general principles in the selection process.
Postural variability given that the control room operators stay seated for longer period of time, they can easily experience reduced levels of alertness and increased risk of fatigue due to reduced blood flow. The implication is a feeling of sleepiness. The control room consoles should therefore be stationed in a manner that allows for change of posture by incorporating consoles that have adjustable heights that will give the operators the option of standing or sitting while at the controls.
Visual comfort there is increased interaction with computers due to the fact that there is increased use of automation in process plants. This implies that the positioning of the visual display units is vital to the successful execution of duties by the control room operators. Therefore, optimal placement of display screens will ensure reduced eyestrain.
Vertical height There are two schools of thought concerning the best possible vertical height for VDUs. The first school of thought argues that the monitors should be placed at a level that is in same position with the eye level.
The widespread use of computer technology in the workplace has resulted in the exposure of workers to the associated hazards related to these relatively new tools. The human interaction with computers requires methods for input such as keyboards and mice can lead to carpel tunnel syndrome and output via visual display Units (VDUs) can lead to visual fatigue.
Process plant VDU operators are required to interact with VDUs users for long periods (as much as 12 hours continuously on a work day) and frequently complain of symptoms such as visual fatigue, head aches, nausea, musculoskeletal pain, and stress. These symptoms can lead to operator error which has resulted in high cost losses in production in industry over the years.
Recognising that light is the medium by which information is transmitted from the VDU to the human eye for interpretation this research paper will focus on the effects of lighting on visual fatigue for process plant operators. Current literature has failed to come to a consensus on a definition of visual fatigue and researchers have relied on a combination of optometry and task analysis to conduct studies that promote their methodology in ascertaining levels of visual fatigue.
For the purposes of this research paper, no new method for measuring visual fatigue will be developed but instead the unique environment of the process plant control room and the variable conditions within that particular environment will be considered. With these variables an experiment using process plant operators will be conducted to validate the hypothesis that lighting affects visual fatigue. Some of the variables that will be considered in the factorial experiment are
Ambient Lighting levels
This will be measured with the use of a calibrated light meter and direct discrete readings are expected. Variation in lighting will be done with the use of rheostats or dimmer switches so that the lighting level can be varied.
Glare in the control room that affect viewing of the VDU
Glare will be measured based on the difference of the image being looked at minus the reflectance from adjacent sources, both readings are expected to be measured via light meters.
Gaze Angle to VDU
Gaze angle will be calculated from trigonometry using measurements of eye level above plane, VDU centre level above plane and the distance from the eye to the centre of the VDU.
Time on Task
Time on task will be measured by stopwatch tasks on the VDU will also be conducted at the same time to ensure the test operator maintains focus on the VDU.
Display Technology
VDUs have evolved over the years and technology across plants varies from Cathode Ray Tube (CRT) screens to Liquid Crystal Display (LCD) screens that can be either passive or active in nature. Review of manufacturers specifications will be done but no active experimentation will be considered other that the varying of actual VDU types.
Resolution
The resolution of VDUs also differs amongst manufacturers, again manufacturers specifications will be reviewed and screen resolutions will be varied
Luminance Contrast
Adjustment of contrast will also be done on VDUs and measured using light meters providing direct data. It is expected that there will be some interaction with glare for this variable.
Based on the results of the experimentation, optimal levels of each variable are expected to be identified. These levels may or may not be the same as currently exists as a best practice right now however the major finding should be, with a reasonable statistical confidence, that lighting effects impact on visual fatigue.
CHAPTER 2 Literature Review
A substantial amount of research has been carried out in an attempt to establish the correlation subsistent between plant accidents and operator fatigue. In most of these studies, it has been pointed out that the results point out to a strong connection between operator fatigue and incidences of accidents in the control rooms. In line with a research carried out in the US by Lamb and Calhoun (2006) under the umbrella of the Michigans Naval Architecture and Marine Engineering Department, human fatigue was found to result from many factors including stress at work, hunger, or boredom among other factors. The researchers found out that fatigue is a serious cause to decreased human performance. Another important finding that the researchers achieved was that accidents occur at a period when fatigue has achieved maximum buildup. Although the research was specifically centered on the sleeping environment of the ship crew, it highlighted how proper lighting in the sleeping environment helps in reducing fatigue among the shipboard operators.
The research carried out by Duffy and Chan (2002) sought to delve the effects of virtual lighting on the operators performance and eye fatigue. In the research, the researchers were determined to find out if different lighting conditions give varying levels of eye performance and eye fatigue. The results of the study pointed to a significant connection between luminance levels and fatigue or eye performance.
In a more recent study, Shen, Shieh, Chao and Lee (2009) sought to underscore the significance of proper luminance on curbing visual fatigue and improving performance. The study is a breakthrough into the understanding of the underlying relationship between change in illumination and eye strain or eye fatigue. Although the study mainly focused on the luminance of the electronic paper displays, it gives a profound understanding of how proper lighting is needed to improve efficiency. In the findings, the researchers concluded that the effects of luminance and the source of light do not pose a statistically significant effect on the visual fatigue though the actual illumination had a strong positive correlation with the performance. That is, efficiency improved when illumination was increased. They therefore recommended that electronic paper displays should be put at greater illumination of 700 lux or higher.
The study by the Cardiff Research Program carried out in 2007 assessed fatigue management in the seafarers. This study aimed to develop best practice proposals that would be apposite in addressing problems of fatigue in the ship type and trade. Measurement of fatigue was met with challenges during this study due to lack of standards in the measurement of fatigue- that is to say, there were no standard measures for fatigue. These challenges made it difficult for any meaningful comparisons to be made with an aim of evaluating the results of research studies that had already been carried out. Thus, such were the gaps that the previous research studies encountered.
Nevertheless, the research was a breakthrough into understanding the relationship between lighting and fatigue among seafarers. In other follow ups, researchers from different corners of the globe sought to address the in-depth understanding of the causes of fatigue in control rooms across the board. All this has been done in an attempt to understand the aspect of fatigue as an imperative challenge to performance in control rooms.
The research study carried out by the Adelaide Center for Research in Australia found that about 20 of accidents occurring in plants result from fatigue of the operators. Health and safety regulations in Europe require that the visual display units be included with measures that are instituted to reduce the effects of fatigue due to lighting in the rooms.
Nevertheless, most of the research works carried out has been instituted to assess the effect of fatigue on operator performance and few of them have endeavored to evaluate the relationship between the lighting system in the control rooms and the operator fatigue even though the findings indicate a positive relationship between fatigue and incidences of accidents.
CHAPTER 3 METHODOLOGY
This chapter gives the methodological approach adopted in achieving the objectives for topic under study. It highlights the intended statistical approach as well as research design and tools that are to be used in achieving the desired objectives. Fatigue is of vital concern and therefore forms integral part of the operator performance in the control rooms and VDUs. Nevertheless, fatigue has a multi-faceted implication and therefore calls for close examination of various issues that relate to this vital element in the performance of operators in their day-to-day business.
3.1 Restatement of the Purpose of the Study
The purpose of the study is to assess the effect of lighting in control rooms by examining how lighting in the visual display units is related to ocular fatigue of the operators so that it can propose optimum levels for the variables investigated to limit visual fatigue for the process plant operators who work in interaction with Visual Display Units. The various variables examined include difficulties in seeing, strange feelings in the eyes, feeling of numbness, feeling tired in the eyes, feeling dizzy and headache. Since the study mainly focuses on the effect of luminance on visual fatigue of operators, it only restricts to constructs that are related to eye strain and fatigue.
The research study employs a random sampling strategy which is also referred to as randomized selection in the study. It employs a true experimental research design where, both the control and experimental groups are selected from the same target institution. This is done so with an objective of reducing the biases that result from effects of extraneous variables (Mulaudzi 2006). Logit statistical method is applied in the study as a primary method of carrying out the analysis of the effects of the youth reentry specialist program.
This method of approach finds good application especially where the study involves estimation of probabilities of success or lack of success from different perspectives. Conditional probabilities are thus able to be established through evaluation and analysis of different characteristics or variables under consideration (Denzin Lincoln 2000).
There are characteristics of the research study that makes it to fit under experimental design. First of all, it uses a systematic manipulation of data collected to achieve the desired objectives of establishing the relationship between the different levels of luminance on the various variables that relate to fatigue of the operators. In addition, various variables are manipulated in various ways to determine their effects on others or their impact on the subject under investigation. For instance, the levels of lux are manipulated through simulation to determine the resulting effect on the operators feeling of numbness, tired eyes, and strange feelings in the eyes among other specific constructs that have been identified to relate to fatigue.
Another characteristic that makes this research design to effectively fit its category is the fact that the researcher used controlled testing, for instance, through selection of samples from the same institution. This is done to establish an understanding of the real relationship subsistent between luminance and fatigue. It is also done to control for the possibility of incurring biases due to extraneous variables.
Lastly, and of course as a fundamental point, the main prerequisite for an experimental design is met when the researcher uses random assignment in the sampling procedure. Random assignment gives the researcher an opportunity to provide each participant in the target group an equal chance of participation or representation.
With respect to strengths and weaknesses of this type of design, an experimental design has a strong capacity of enabling the determination of the cause-effect relationship in the variables under study or the variables being manipulated and controlled. On almost related ground, the fact that manipulation and control involves selection of the variables before they are subjected to experimental aspects of manipulation, control and observation, if the right variables are not identified, the entire research would be rendered as good as a waste of research time as it will not bring a meaningfully intended contribution (Bryman Bell 2007). The experimental design used in this research study will therefore help the researcher to assess the following
The effect of lighting on visual fatigue for Process Plant Visual Display Unit (VDU) Operators
Factors that interact with lighting to contribute to fatigue for operators in process plant visual display units the influences that architectural designs can have in the effect of lighting on fatigue
3.2 Validity
3.2.1 Internal Validity
Internal validity of the research is low as with most field research. A number of factors are likely to impact on the response of the respondents. Some of the factors that have been identified to cause an impact on the internal validity of a study include the following. First, reactivity effects or the Hawthorne effects may have an impact on the internal validity where they respond, not because of the procedures of the study but simply as an independent response or reaction to being studied. For instance, in the Hawthorne study, the researchers found though they had created different environments for the employees, the workers productivity just kept increasing. They hence made a conclusion that the workers were merely responding, not because of the experimental conditions that had been created but because of their awareness of being studied.
Another notable threat to internal validity is selection bias. Since participation in the study by respondents is voluntary, selection bias is likely to affect the internal validity. Wood and Haber (2009) note that in most studies in which target respondents decide themselves whether they wish to participate or not face the impact of selection bias. Instrumentation is also identified by the scholars as another factor that affects internal validity. In this threat, any change or alterations made in the measurement of variables or changes in the techniques of observation may justify changes in the measurement that is ultimately obtained. A good way of dealing with this threat is to ensure consistency of the instruments used and techniques applied in the study. As such, the lux levels must be maintained at an exactly desired level for all the participants.
Another threat that may cause considerable impact on the internal validity of this research study is hypothesis-guessing threat. This threat is exhibited where the respondents base their response and behavior on what they perceive the study to be about hence responding as a reaction to the study rather than just response to the survey program. The researcher will minimize the impact of this threat by clarifying to the respondents the concepts of the study before the actual study commences.
A history threat may also pose a threat to the internal validity of the study. Given that the study examines effects of luminance on ocular fatigue in a large organization based on various levels and variables, historical events that might have taken place in the recent past may influence the outcome. This threat to internal validity is often experienced where such interfering events happen between the pre-test and post-test.
Since the researcher intends to make a prior request to the administrators in the organization under study and to the relevant authorities, another threat that may come in play is the testing threat where participants carry out their own research which may affect the actual study by acting as a pre-test study. Mortality threat may also hamper the credibility of the internal validity where respondents drop out of study leading to an inflated measure of the revealed effects.
These threats will be addressed through randomization or randomized selection, careful and systematic consideration and elimination of alternative causes of particular responses as much as possible and putting plausibility into consideration.
3.2.2 External Validity
The external validity relates to the extent to which the results of the study can be generalized to particular populations, settings or times for instance, where there is true random sampling of the respondents with random assignment. It also relates to the extent to which the results of the study could be generalized across particular populations, settings and times. This is a serious threat to external validity since the results of the study may not hold across all groups despite the use of true random sampling. The salient threats to external validity of the study are related to the extent of generalization that can be drawn from the study. However, to rule out effects of extraneous variables, randomized selection is done. First, whether the results of the study can hold for all times is a threat that sprouts from the interaction of history and treatment. Secondly, the interaction of selection and treatment poses the uncertainty of whether the results of the study stand across all groups. Lastly, it may be uncertain whether the results of the treatment may hold across all settings.
In order to reduce the impacts of the threats to external validity, the researcher has identified the target population for the study. In addition, the researcher will ensure that the samples sampled out are representative.
3.3 DATA ANALYSIS
3.3.1 Statistical data analysis
Items or questionnaires that do not receive response will be coded as missing values. Scale values will therefore be calculated as the average or mean of the single items. All items are assumed consistent with characteristics of a normal distribution.
Descriptive statistics and Analysis of Variance (ANOVA) was performed to evaluate whether there is significant relationship between fatigue-related factors and changes in the lux levels (Ayelet, Lingard Levinson 2008). The relationship between the various variables will be measured through the Pearson product-moment correlation coefficients (Grinnell Unrau 2007).
A run of frequencies for the responses is carried out to determine the variability of the responses and the centrality which enable a conclusive report to be drawn thereafter from the results. The standard deviations will be used to measure variability in the responses of the operators concerning various constructs being investigated. For that matter high standard deviations will be interrupted to imply that there are high variability in the reports.
The statistical package for social sciences (SPSS Version 16.0) is used in all the statistical analyses carried out.
RESULTS
The following are the results of the analysis of the experiment that was carried out. The researcher analyzed the data with respect to the frequencies and also carried out an analysis of variance (ANOVA). The analysis of variance or ANOVA was helpful in offering a succinct comparison of the various means recorded in the experiment at various levels of lux. As such, this analysis helped to rule the possibility of the difference or variations in means being caused by any other factor other than chance (Stevenson 2008).
In order to enable both intra and inter-variable comparison, the analysis also included variable splitting where the results of the analysis were split on the continuum of the start of the session and the end of the session and then with respect to the various lux levels. In addition, the ANOVA was of particular help since it helped in testing if the operators had the same averages at different lux levels for the different variables that were subject of assessment in the study. Although this hypothesis was not actively proposed for testing as part of the hypotheses, testing for it enabled the researcher to rule out differences in sample characteristics to be the cause of any difference in means as it would arise after analysis.
The results of the analysis had various implications. The analysis for the lux level at the start of the testing period produced a lux mean of 321.43, with a standard deviation of 125.357 and a variance of 15714.286. at the same period, a run of frequencies for thee various variables indicated that most of the operators exhibited a dizzy feeling with a mean of 4.86 with a standard deviation of 2.0222 and this was followed by those who experienced headache at the same lux level. An average of 4.64 of the operators exhibited a headache and a standard deviation of 1.833. The mean for those who felt numb at these aggregated lux levels was 4.11 with a standard deviation of 1.637.
However, analysis of the percentiles at different lux levels showed that when the operators were exposed to a lux level of 500 the number who reported a dizzy feeling increased as compared to a lux level of 300. Similarly a lux level of 300 produced greater dizzy feeling among the operators than at a level of 175. None the less, the operators averagely had no distinctive feelings at lower lux levels but as the level of lux was increased gradually hit can be seen the change this caused on a variable like the dizzy feeling, headache and feeling of numbness. The results of the analysis can be seen in the above table.
The following table is however a comprehensive analysis for the variables at different levels of lux. This analysis slightly differs from the above one given that in this analysis the different lux levels formed the split output definers for the purpose of sorting the analysis on the basis of each level of lux as compared to the aggregated level. At a lux level of 175, the mean of those who felt difficulties in seeing was 1.94 individuals. The total number of participants at this level was 16. The mean for those who had strange feelings in the eyes was 3.19. This clearly shows that it is greater than the mean for difficulties in seeing but less than those who felt numb (mean 4.19), dizzy (mean 5.12), and headache (mean 4.50).
At a lux level of 300, the mean for the difficulties in seeing reduces from 1.94 to 1.62. This shows that at level of 300 of lux the operators experienced less difficulties in seeing as compared to a level of 175 of lux. It is worth noting that the standard deviations at the various levels differ. At lux of 300 the standard deviation for those who had difficulties in seeing was 0.824 while it was 1.237 at 175 lux. This results from the different values of N (the proportions of the sample who participated at those levels differed). At 175 lux, the sample size was 16 while at 300 the sample was 24 thus reducing the level of variance.
When the lux level was increased to 500 for the same variable of difficulties in seeing, it can be seen that the mean of those who indicate a feeling of difficulties in seeing is 1.94 and the same value was recorded for the lux level of 175. A note of the difference in standard deviations should however shed more light in the gravity of the difficulties in seeing. At lux of 500 with a standard deviation of 0.824 it is evident that the level of difficulties could be higher than the 175 lux level even though the sample sizes were same. The deduction is that there is less standard error in the results at 500 than those at 175 even if the sample sizes are same and means equal.
With respect to strange feelings in the eyes, the mean of those who feel strange in the eyes is 3.19 with a standard deviation of 1.13. As the lux level is increased to 300 the mean slightly changes upward to 3.62 and the standard deviation also increases to 1.74. A further increase of the lux level to 500 leads to a reduced mean of 3.44 with a 1.031 standard deviation. On the other hand, the mean of those who experienced tired eyes at lux level of 175 was 2.38 with a standard deviation of 1.31. When the lux level is increased to 300, the mean increases to 3.17 but the standard deviation also increases tremendously to 2.180. This indicates that even though the mean number of operators who felt tired eyes increased, there was also a large variation in each operators reports about how they felt with respect to tired eyes. Their feelings had wide variability. That is to mean that the individual measures highly deviated from the mean and hence indicate a high level of standard error. With respect to feeling numb, a lux level of 300 produced the least average score for those who felt numb. Even the standard deviation at this level was lower than other levels. Thus while at 300 lux level those who felt numb had an average of 3.92 and a standard deviation of 1.558, the other lux levels had scores of means of 4.19 and 4.31 and standard deviations of 1.870 and 1.580 for lux levels of 175 and 500 respectively. Thus, it is evident that at lux levels of 300, the operators experienced the least feeling of numbness.
Then, the analysis also generated results for dizzy feeling and headache among the operators at the different lux levels. At a lux level of 175, the mean of those who felt dizzy was 5.12 and the standard deviation was 1.996. The mean reduced to 4.83 at 300 lux. The standard deviation at the same level was an increase over the one recorded at 175 lux. It was 2.057. When the lux level was increased to 500, the mean further reduced to 4.63 and the standard deviation slightly increased to 2.094. thus, the reduction in the mean is outweighed by the increase in standard deviation as the increase in standard deviation denotes an increase in the variability of individual feelings among the operators. With respect to headache, a mean of 4.50 is realized with a standard deviation of 1.414 at 175 lux level. The mean increases by a 0.29 point when the lux level is increased to 300. The measure of variability increases to 1.841. So, it is deducible that with respect to headache at the start of the experiment session, lower lux levels produced lower levels of headache.
The analyses for the variables were also done at the end of the operator shift. The table below offers the comprehensive results in a briefed version. At the end of the operator session, looking at the mean of those who experienced difficulties in seeing at 175 lux, the mean is 4.75 and standard deviation is 1.291. This is a considerable increase in the number of those who have difficulties in seeing if we compare the end and start of the session. At the start, the mean was 1.94 and standard deviation was 1.237. The standard deviation shows no significant change and thus means that the individual scores were clustered around the mean. That is, most operators exhibited feelings of strain in vision. At a lux of 300 the mean at the end of the operator session is 3.29 with a standard deviation of 1.301. This is lower than that recorded at 175 lux level and almost double the level recorded at the start of the session. At lux 500, the mean again increases over that recorded at 300 lux though it is higher than that recorded at the beginning of the operator session.
Looking at those who had strange feelings in the eyes at both the start and at the end of the session at various level of lux, there is clear indication of an increase in the means if the results for the end of session are compared against those recorded at the beginning of the session. At lux level of 175 the mean is 5.38 with a standard deviation of 2.125 but these figures reduce considerably when the lux level is increased to 300. The standard deviation reduces to 1.204 from 1.740 observed at the beginning of the session. Thus at lux level of 300, the number of operators who report strange feeling in the eyes tend to concentrate around the mean hence implying that most of the operators have a reduced strange feeling compared to that observed at lux level of 175. As the lux level is increased to 500, there is a marginal change in the mean number of operators with strange feeling in the eyes. In contrast, the standard deviation reduces indicating less variability in the reports of the operators with respect to the strange feeling in the eyes.
The mean of those who feel tired in the eyes remain high and equal for lux levels of 175 and 500 where the means equal 5.81 in both cases. However, at 175 lux level, there is a high variability as seen from the high value of standard deviation. The mean number of operators who exhibit tired eyes at lux 300 is not only lower but even the variability is lower than the other levels.
The trend for numbness is almost in a similar direction as that recorded for tired eyes. Lux levels of 175 and 500 record high means for numbness with high variability observed for level 175. Still, 300 lux level records the least feeling of numbness among the operators. The observations for those who feel dizzy and those who feel a headache also follow the same trend. Less means are recorded for 300 lux levels while higher means are observed at the other lux levels.
Based on the results of the analysis, there is evidence that at a lux level of 300, there were fewer reports of fatigue related constructs like eye strain, headache, dizzy feeling, numbness, and difficulties in seeing. For instance, looking at those who had strange feelings in the eyes at both the start and at the end of the session at various level of lux, there is clear indication of an increase in the means if the results for the end of session are compared against those recorded at the beginning of the session.
Ocular fatigue is characterized by difficulties in seeing, a dizzy feeling, numbness and headache. It is therefore evident that the optimum levels of lux are imperative to ensure that the operators do not experience these characteristics which indicate a presence of ocular fatigue. At lower lux levels, the eyes strain and thus the operators get fatigue which hampers their ability to operate with desired proficiency. In such a case where the operator feels dizzy, falling a sleep may easily lead to accidents.
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