survey effect of illuminance source on alertness in a laboratory design

Background and aims: Workplaces with poor lighting conditions often created occupational accidents or illness. This occurs because light cause visual and nonvisual effects on numerous physiological variables, such as the human sleep-wake cycle and cognitive performance. Indoor lighting conditions, as one aspect of the work environment, Influence on occupant’s mood, well-being, task performance and work engagement. Greater satisfaction in case of lighting conditions at workplace is usually depending on higher work plane lighting, lighting uniformity, absence of glare, light directionality (ratio of horizontal and vertical illumination), as well as the presence of a window. Thus, selecting suitable lighting system is an important part of increasing productivity in the office work plan. Although Fluorescent lighting is a conventional system in a range of industrial and domestic applications, but newer technologies such as light-emitting diodes (LED) have begun to attract as one of the most promising candidates for sources of general illumination in the near future. This is due to variety of advantages such as lower power consumption, longer usable lifetime, greater eco-friendliness due to do not contain mercury and easier processing due to their small size and adaptable shape. Due to significant growth of the LED technology and the possibility of their replacement with Fluorescent technology, it is important to evaluate the effects of these modern lighting options on worker performance. In fact, lighting can cause acute emotional, behavioral, and cognitive problems. These effects of light may be dependent on parameters such as intensity, power, and type of light source. The aim of this study was to compare the effect of fluorescent and LED light sources on the alertness, cognitive performance and visual comfort level among student in a laboratory environment. Methods: Twenty eight participants (19 to 35 years of age) were recruited to participate in this study. All participants were screened for health problems, especially about neurological diseases, mental and visual disorders. Test environment is a room with dimensions of approximately 2 x 3 x 3 meters and without natural light (with no window). All lighting sources were installed on the ceiling of room test. 4 fluorescent tube lamp on the right side and 9 white LED lamps on the left side of room were installed. Under each of lighting source a table and chair to carry out the defined tasks were placed. Turn on/off button each of lighting source also is separate. This characteristic is extracted from the booklet of lamp Manufacturers. For each participant in the study, a series of tasks and tests to measure the level of alertness, cognitive performance and visual comfort was designed. EEG method was used to measure the level of alertness. For this purpose, NeXus-4 device was used for data collection. The NeXus-4 is a small and high-end biofeedback and neuro-feedback system which is totally suitable for professional grade physiological monitoring, and clinical applications. Data processing, digital Signal filtering, Trends report and statistical analysis is done by the Bio Trace software that is compatible with the device. Using this device, signals the brain activity of the participants were recorded. Nexus-4 takes advantage of active Noise Cancellation technology, where artifacts and external interference were reduced and provides high-quality EEG signals. Electrodes were placed on subjects’ scalps according to the International 10-20 system. According to the instructions of device, reference electrode on the left ear was placed. Ground electrode (white) on the right ear and red electrode on the point Cz of the head (located in the occipital region) was placed. Gamma frequency range 35-45 Hz, beta frequency range 13-21 Hz, alpha frequency range 8-12 Hz, was set on the device.  One goal of the study was to evaluate the effect of two different lighting sources (LED and fluorescent) on participant’s performance during a computer-based visual task. For this purpose, “Freiburg Visual Acuity & Contrast Test” (FrACT) was used. In this method, participants by viewing the computer screen determine the orientation of ring and give the appropriate response via the computer keyboard as soon as possible. Then for each step, a performance indicator for contrast and visual acuity test were determined as follow calculation: (Total number of correct responses / Total duration of step). In following, the contrast and visual acuity threshold was determined by the software itself for each participant. For carry out this task, an experiment was used that proposed in 1999 by the Courret. Just as computer-based tasks, Landolt rings were used for paper-based tasks.  The participants of this study received a sheet of white paper on which 96 Landolt ring was printed in grey (very low contrast), and they were asked to determine as quickly as possible the correct orientations of all the 96 rings by writing down the number counted each ring in the bottom of the page. Then, the number of errors was counted as a performance of paper-based tasks for two lighting environments. In addition, participants in this study had to express our visual comfort under two lighting sources. For this purpose, Office Lighting Survey (OLS) was used to evaluation the satisfaction of participants during each lighting sources. OLS is a simple, valid, reliable questionnaire-based assessment method for human satisfaction regarding office lighting. This questionnaire was presented by Elkland and Boyce in 1996. Participants in this study were asked to express their satisfaction or dissatisfaction of existing lighting sources with  each statement by using the 4-point Likert scale with no neutral choice (yes, rather yes, rather no, no). Result: the results obtained during the computer-based tasks under two different lighting sources. For both fluorescent and LED lighting source, average performance efficiency is 0.66 and 0.64, respectively. There was no statistically significant difference between the two different lighting conditions (p=0.13). A comparison of the average contrast threshold obtained during the contrast test between the two sources of lighting. For both fluorescent and LED lighting source, average contrast tests obtained 0.52 and 0.45, respectively.  Again no statistically significant difference was observed between the two different lighting conditions (p=0.356). The results obtained during the paper-based tasks under two different lighting sources. The average of error in the identification of ring’s orientation is more in LED lighting source than fluorescent lighting source. There was no statistically significant difference between the two different lighting conditions in orientations of up (P = 0.074), down (P = 0.896), right (P = 0.713) and left (P = 0.246). Also, the average number of error for all Landolt-ring orientations under two lighting sources. On average, under the fluorescent lighting, 3.93 rings and under the LED lighting, 4.93 rings were incorrectly identified by the participants. Comparing the average error in orientations of Landolt-ring show was no statistically significant difference between the two lighting conditions (p=0.1≥0.05). The results of subjective visual comfort represented that the maximum difference between tow lighting source in the second question (Q2) (In general, the lighting in this office is comfortable), Q3 (This color of light allows me to carry out the different tasks) and Q4 (My skin looks natural under the light.) were observed. Also statistical analysis showed a significant difference to these questions Where p-value was equal to Q2 (0.001), Q3 (0.011) and Q4 (0.003). The results of questionnaire analysis (subjective preferences and visual comfort) showed that the fluorescent lighting (66.83 points) was most preferred by the participants than LED lighting (51.83 points). There were statistically significant difference among the two lighting source where fluorescent light was significantly better preferred to LED light (p = 0.002). In terms of visual comfort, fluorescent light (68.1 points) was most comfortable than LED light (67.33 points) but there was no statistically significant difference between two lighting conditions (p = 0.6). Electroencephalograms mean relative power for alpha, beta and gamma frequency band at the CZ electrode were recorded. The mean relative power of frequency bands of all participants for LED lighting condition is more than fluorescent lighting condition. Also, in between three frequency band, alpha and beta bands were the biggest values. For gamma frequency band, T-test revealed that each lighting condition showed no statistically significant difference on alertness level of participant (p=0.24). Statistical analysis for alpha and beta frequency band showed a significant difference between two lighting source. Conclusion: In general, participants in this study reported that they most comfortable in fluorescent lighting conditions and more preferred this lighting source than LED lighting source. Performance of participants in paper-based task was significantly better under the fluorescent lighting condition than under the LED lighting condition. Under fluorescent lighting conditions, participants on average 3.93 rings and under LED lighting condition 4.93 Ring incorrectly identified. This results show that Participants to carry out paper-based tasks under the LED lighting sources more likely commit to make errors. Even though these errors were not statistically significant, it can be inferred that the light source (fluorescent or LED) have a little effect on the carry out of paper-based tasks and the most important cause of error during cognitive tasks is the brightness level and individual variables such as age. The participant’s performance in the computer-based tasks under fluorescent lighting source was better than LED lighting source. Visual acuity and contrast threshold of participant’s under fluorescent lighting conditions is better than LED lighting conditions. But no statistically significant difference was observed. In other words, we can conclude that participants while performing computer tasks did not show better or worse performance under both lighting source. These conclusions indicate that the light source (fluorescent or LED) does have little impact on computer-based tasks. Also similarly studies carried out by Linhart et al. (2011) and Shamsul et al. (2013) that don’t show significant difference in visual acuity and contrast thresholds users and this may indicate that the FrACT test is not appropriate for this particular field. During the assessment of subjective visual comfort, the first question (I like the lighting in this office) scored satisfaction of 75% for fluorescent lighting source and 61% for LED lighting source. The second question (In general, the lighting in this office is comfortable.) scored satisfaction of 74% for fluorescent lighting source and 52% for LED lighting source and there were statistically significant difference among the two lighting source for this question. As a matter of fact, only the differences in statements of Q2, Q3 and Q4 are statistically significant that’s shows participants in this study subjectively most comfortable in fluorescent lighting conditions than LED lighting source. However, the absence of significance in other cases may be due to the small number of study participants. As regards the questions of visual comfort questionnaire was designed based on two dimension preference and visual comfort, the results of comparison these two dimension show that fluorescent lighting to LED lighting is the most preferred and the results are statistically significant. Comparison the visual comfort result of the participants also showed that fluorescent lighting to LED lighting is the most comfortable sources but this was not statistically significant. The results suggest that 50% of the participants prefer fluorescent light to LED light for carry out cognitive tasks. In this study, we analyzed the EEG spectral power measured on the participants in order to compare the effects of LED and fluorescent lighting on alertness. In our study, results showed that the EEG power for alpha, beta and gamma frequency bands for LED lighting are more than fluorescent lighting. This increase in the range of alpha and beta frequency bands was significant. This indicates that LED lighting could disturb human alertness in compared with fluorescent lighting. Hawes et al. recently shown that, the LED lighting in compare with the fluorescent lighting may have positive effects on perception, cognition and affective state. However, our results proved the opposite of this report. In contrast, our results indicate that the LED lighting have significantly effect on the alertness, cognitive performance and visual comfort level. As we examined only some short-term effects of LED lighting in a small community and long-term effect should be studied in the future.