Effect of light color temperature on selective attention, error rate and reaction time

Investigating the effect of light color temperature on selective attention, error and human reaction time Abstract Background and aims: In humans, the reaction time limit is associated with several factors. It includes the time that takes to stimulate the sensory member, the stimulus effect is transmitted to the brain, then is perceived and the decision is made; consequently, the command resulting from the decision of the brain is sent from the brain to the functional member, and the member operates. Failure to respond at the right time may result in human error and the occurrence of incoming incidents. There are important factors that affect the reaction time. Attention is one of the important factors affecting the speed of the reaction. Selective attention and correct perception of several stimuli among the other stimuli is one of the effective factors in promoting productivity and safety. Additionally, various environmental factors may be effective in determining selective attention, increasing the number of errors and the human response time in detecting triggers. Environmental lighting is one of the factors affecting the processing mechanisms of the brain. In the design of indoor and outdoor lighting systems, the quality parameters of the lighting system are usually less considered. Color temperature is one of the most important qualitative parameters of light, which is measured by the Kelvin unit and is an indicator for the brightness and color of the light. The aim of this study was to investigate the effect of color of light temperature on selective attention, error rate and reaction time.  Methods: This research is an interventional and laboratory study in order to determine the effect of the color of light temperature on human error, selective attention, and reaction time of students in Tarbiat Modares University (TMU) of Tehran during the fall of 2018. All students were in the same age range. The inclusion criteria for the study were; not having any eye-related diseases, such as diminished vision and subtlety, and mental-psychiatric disorders. On the day before performing the test, individuals were urged to have enough sleep and rest, to adhere to a regular diet, and to avoid taking medicines, coffee and caffeinated drinks. In this interventional study, 92 students (36 female and 56 male) from Tarbiat Modarres University of Tehran with an average age of 28.33 years were recruited as subjects. The measurements and tests related to selective attention and reaction time of individuals were performed in 4 locations with an equal lighting system and different color temperatures (3500, 4000, 5000, or 6500 degrees Kelvin). In the first stage of the study, in order to determine the effect of the color of light temperature on the studied parameters, the participants were randomly divided into four groups with 24 subjects in each group. Before the main test was being performed, the subjects were kept in rooms adjusted to a brightness of 3500° K to rest for at least 5 minutes in order to be adapted to the situation, and then, in the same conditions, to become familiar with the test method they were studied with the Stroup software. In the second step, each group was placed in a separate room where the levels of brightness had been designed with one of the lighting systems to yield a color temperature of 3500, 4000, 5000, and 6500° K. Cognitive performance tests including reaction time, accuracy and selective attention were measured using Stroop tests. Measurement of interference score and interruption time, which are indicators of selective attention, were calculated by measuring the difference in the error rate and the reaction time in detecting incongruent and consonant words. Stroop test was used to determine the reaction time, error and other parameters. This test consists of two parts; the practice and the main test, each of which has 3 stages. The first step is to name the color in which circular shapes appears in green, blue and red colors and the participant, upon viewing the image, applies pressure on keyboard buttons which are labeled with colors corresponding to the ones on the screen. The second step is to name the word which appears in a white box. The names of the colors appear, and as soon as the correct word is recognized, the person being tested should press the color word associated to the word on the keyboard. The third step, which is the main stage of the test, is a non-consistent word (red-green-blue) shown randomly and sequentially on the monitor's screen. The subject must only press the keyboard button with the same color, only emphasizing the color and regardless of its connotation. In this test, 48 matching colored words (the color of the word is identical with the meaning of the word; red, yellow, green and blue) and 48 non-consistent colored words (the color of the word is not the same as the word meaning; for example, the blue word shown in red). The time lap between the stimulants was 800 milliseconds and the duration of each of them was 2000 milliseconds. The subject's task was to select the correct color only. Finally, the data were analyzed using SPSS software. Results: Based on the results of this study, the highest mean of correct selection (474.49 ± 10.65) and the lowest mean of the correct ones (654.49 ± 11.77) were assigned to the color temperature of 6500 and 3500 ° K, respectively. Also, the highest mean, the error (15.65 ± 9.77) and the lowest mean error (10.94 ± 9.4) were reported at a color temperature of 3500 and 6500 ° K, respectively. According to the results of this study, with an increase in the level of color temperature from 3500 to 5000° Kelvin, the number of questions that were not responded decreased. Likewise, the number of unanswered questions for the color temperature of 6500 °K slightly increased compared to the color temperature of 5000 and 4000 °K. The results also indicated that, with an increase in color temperature from 3500 to 6500 °K, the reaction time to visual stimuli also decreased. The highest interference score was in the light color temperature of 3500 °K which suggests that the number of faults in subjects in naming inconsistent words relative to consonant words at a color temperature of 3500° K was high compared to the other color temperatures. Also, according to Fig. 3, the maximum interference time at light color temperature is 6500 ° K. This suggests that the performance time of the subjects in naming incoherent words relative to consonants at a color temperature of 6,500° K compared to other color temperatures was more significant. Although the average response time under lighting condition with color temperature of 6500° K (718.95 ± 65.33) was less than the color temperature of 3500° K (728.58 ± 43.48), according to the results of the study, with a decrease in color temperature, the increase in mean response time was observed, but this difference was not significant (p <0.05). In the present study, we compared the mean of the studied variables (interference score, interference time, correct number, number of errors, unanswered items and response time) among classified groups tested under different lighting conditions with color temperatures (3000, 4000, 5000, and 6500 degrees Kelvin). One-way ANOVA was used for data analysis. Based on the results of Tukey's post-test, the mean of correct responses under lighting conditions with a color temperature of 6,500 ° K was significantly higher than the other color temperatures, and the average for the number of correct responses at the color temperature of 5000 was significantly higher than 3500 and 4000° K (p <0.05). The average light error rate with a color temperature of 6500 ° K was significantly lower than the mean error at color temperature of 3500 and 4000 ° K, and also the average error under lighting condition with a color temperature of 5000 K was significantly lower than 3500 and 4000 ° K. 0> p). Also, based on independent t-test (Table 2), there was a significant relationship between subjects’ gender and variables such as interference score, interruption time and number of unanswered questions. For all of these three variables (interference score, interruption time and number of unanswered questions) mean in men was significantly lower than women (p <0.05). Based on subjects’ gender, the average response time under different color temperatures showed that the response time (or reaction time) of female students under lighting conditions with 3000 and 5,000 ° K was higher than that of male students, while under lighting conditions with 4000 and 6500° K the response time of male students was higher than that of female students. Although the average response time under different color temperatures was different between male and female subjects, based on the results from independent t-test, such difference was not significant. Conclusion:  In general, the results of the study showed that when subjects are exposed to a light color temperature of 6,500 ° K, the number of correct responses by them is higher than those exposed to other color temperatures, and with increasing the color temperature of the light source the number of correct answers increases. Also, according to the results of this study, the levels of error decrease by increasing color temperature of light source. Based on the results of this study, it is suggested to make use of light sources with a color temperature of 6,500 ° K in designing the lighting system of the places where human reaction time and error are of great importance. Accordingly, it is recommended to repeat this study in other demographic groups, as well as taking into account the qualitative parameters of the lighting system in addition to its quantitative parameters. Keywords: color temperature , light, selective attention, reaction time