Classrooms' indoor environmental conditions affecting the academic achievement of students and teachers in higher education: A systematic literature review

Abstract This study reports the outcomes of a systematic literature review, which aims to determine the influence of four indoor environmental parameters — indoor air, thermal, acoustic, and lighting conditions —on the quality of teaching and learning and on students' academic achievement in schools for higher education, defined as education at a college or university. By applying the Cochrane Collaboration Method, relevant scientific evidence was identified by systematically searching in multiple databases. After the screening process, 21 publications of high relevance and quality were included. The collected evidence showed that the indoor environmental quality (IEQ) can contribute positively to the quality of learning and short‐term academic performance of students. However, the influence of all parameters on the quality of teaching and the long‐term academic performance could not be determined yet. Students perform at their best in different IEQ conditions, and these conditions are task‐dependent, suggesting that classrooms which provide multiple IEQ classroom conditions facilitate different learning tasks optimally. In addition, the presented evidence illuminates how to examine the influence of the IEQ on users. Finally, this information supports decision‐makers in facility management and building systems engineering to improve the IEQ, and by doing so, allow teachers and students to perform optimally.

and the institutional and structural features of the school environment. 2 This is also a challenge in the education at a college or university, hereafter referred to as higher education. 3 To facilitate the school climate, higher education school management provides buildings, assets, and services for their employees and students. The role of facility management (FM) is to coordinate and maintain these assets and services. 4 By doing so, FM influences a school's ability to act proactively and meet all requirements to create a positive school climate. 4 A positive school climate is associated with students' healthy development and the retention of teachers, and can even have a predictive value for the academic achievement of students. 1 In order to improve the effectiveness of this climate, FM has an active role in creating an optimal learning environment. This requires, among other things, appropriate ventilation, heating and air conditioning, ample forms of lighting, necessary acoustical control, and upkeep of maintenance. 2 This study focusses on the indoor environment, which is a system of the indoor air quality (IAQ), thermal conditions, acoustic conditions, and lighting conditions. 5 Many factors may influence the academic achievement of students, 6 but the indoor environmental quality (IEQ) in classrooms can potentially influence teaching and learning positively, 7,8 which in turn increases the likelihood of a better academic achievement of students ( Figure 1). 2 The IEQ addresses the subtle issues that influence how users experience an indoor space, for example, a classroom. 9 The IEQ results from a variety of pollutants or other determinants that can be caused by all four indoor environmental parameters. In this context, occupants' comfort depends on the actual indoor environmental conditions and personal demographic characteristics, such as gender and age. 5 In addition, it depends on psychobiological processes, such as arousal and stress, and psychological processes, such as perceived control and attention. 10 Moreover, the IEQ to which teachers and students are exposed, can affect teaching effectiveness and instructional practices, 7 which in turn can affect students' academic achievement. 2 A study of Kok et al 11 showed, for example, a statistically significant positive relationship between teachers' perceptions of classrooms' lighting and acoustic conditions and study success. Also, the IEQ can influence users' task performance, communication and social interaction, mood, and health and safety at school. 2,5,12 This influence has often been examined by analyzing the effect of one parameter. 5 In 2016, Wargocki and Wyon 8 analyzed the combined effect of thermal comfort and IAQ on humans' short-term cognitive performance. These researchers identified the following human mechanisms which are affected by both thermal and IAQ conditions: distraction and attention, motivation, arousal, neurobehavioral symptoms, and acute health symptoms. Moreover, lighting conditions, for example, can affect mental alertness and cognitive performance 13 ; and annoyance and distraction can be caused by poor acoustic conditions. 14 Furthermore, a poor IEQ can cause adverse health outcomes, which can cause sick leave and impaired academic achievement. 15 Students' academic achievement also depends on how teachers use all resources to improve in-class activities. 2 Finally, it depends on the students' ability to concentrate and think clearly, as these aspects together influence the in-class academic performance of students. 8 Therefore, to assess both the individual and the combined influences of all four indoor environmental parameters on the quality of teaching and learning and students' academic achievement is a worthwhile exercise.
At this moment, there are no specific guidelines available for higher education school buildings. The focus of earlier research, for example addressing the IAQ, was mainly on pupils in primary and secondary education. 16 Based on the outcome of this research, specific IEQ guidelines for pupils of primary and secondary schools were developed. 17 However, facilitating young adults (aged 18-25 years) and teachers (aged 25-65 years) in higher education might require a different IEQ in which they can perform optimally. In order to support initiatives, which aim to develop specific IEQ guidelines for higher education school buildings, this review aims to provide an overview of how classroom indoor environmental conditions influence the quality of teaching and learning and students' academic achievement in higher education.
The following research question is explored in this review: What is the effect of IEQ in classrooms in higher education on the quality of teaching and learning, and students' academic achievement? In addition, three hypotheses will be examined: (a) the IEQ influences the quality of teaching; (b) the IEQ influences the quality of learning, and (c) the IEQ influences the students' academic achievement.
In addition, in the context of this study, the quality of teaching and

Practical Implications
• Over the last decades, research has shown that classroom conditions in schools are far from optimal. In some cases, conditions can even be unhealthy and affect teachers' and students' performance adversely. When students do not perform to the best of their ability, this can have serious consequences for the individual and society.
• European and Dutch authorities recognize the need for better classrooms and stress its urgency. The gathered evidence in this study helps all involved to understand the extent of the influence of the IEQ on educational processes and outcomes. It can form the basis for better-informed decision-making, especially for those who are involved in renovation or new construction of school buildings for higher education.
• Specifically, facility management (FM) and building-related engineering partners of FM can use this information to design a more user-oriented built environment.
By doing so, this increases the likelihood of classrooms in higher education supporting educational outcomes.
Moreover, this potentially allows future generations of teachers and students to perform and learn better in a healthier environment. learning is operationalized by how teachers and students perceive teaching quality, learning quality, and their physical and mental health. Students' academic achievement refers to their short-term and long-term academic performance. 2 Short-term academic performance is often quantified with cognitive performance tests or with the use of school exercises. 8,18 Long-term academic performance focusses on the performance of students for a course or academic year. 19,20

| ME THODOLOGY
We applied the Cochrane Collaboration Method to identify relevant literature for review. 21  The search through the selected databases yielded 2501 publications, which were imported in RefWorks. After removing duplicates (n = 608), we analyzed the relevance of the selected publications. When the title, keywords, or abstract did not give any indication that indoor environmental conditions were studied, the publication was excluded (n = 1512). These publications emerged in the primary search because one or more keywords were used in a different context. For instance, a study used the word "light" or "noisy" as an adjective, or the word "illuminate" was used as a synonym for "illustrate" or "embellish." We also excluded publications that addressed only the physical indoor environmental conditions, or other types of building performance (eg, energy consumption and sustainability) without analyzing the effect on teaching, learning, or academic achievement (n = 135). Finally, we excluded publications that addressed humans with physical or mental disabilities (n = 44), and publications that did not address classrooms in higher education (n = 131). All publications not written in English were excluded (n = 8). In total, 63 publications were included after this selection stage.
As a final selection stage, the relevance and quality of the 63 remaining publications were determined. To assess the relevance of the included publications, the context and scope of the study were assessed. The context of the study was high when the influence of multiple indoor environmental conditions on the quality of teaching, learning, or academic achievement was analyzed. In addition, the scope of the study was high if the study analyzed indoor environmental conditions and assessed the impact of these conditions on the performance of teachers or students. Moreover, the reliability and the methodological quality of the study were analyzed to assess the quality of the study. The reliability of the study was high when it was published in a peer-reviewed journal and provided detailed information about the sample (eg, sample size, gender, age, and standard deviation). The methodological quality was high when the methodological section in the study described in detail how the research was conducted and when the applied tests or questionnaires were available (eg, appendix and website).
In addition, this quality was high when the study provided detailed information about the accuracy of used measuring equipment and how the measurements were performed in the classroom (eg, position, number of measurements, and measuring height). Finally, the methodological relevance was high when three or more key performance indicators of the targeted four indoor environmental parameters were measured, because these studies may reveal, in particular, the combined influence of the indoor environment.
Independently, the authors scored publications, compared the individual scores, and adjusted the rubrics of the assessment tool.
Appendix 3 presents the authors' final version of the assessment procedure, which was used for scoring the relevance and quality of all publications. The context, scope, reliability, and methodological quality scores were expressed in a percentage of the maximum score (100 percent). Studies with a relevance and quality (RQ) score lower than 60 percent were excluded (n = 44). Through hand-searching, using the title of the study in Google Scholar, two additional studies have been identified. These studies addressed the same research as the, through the systematic search, identified publication; however, they contain additional and relevant information. The first study added is the doctoral thesis of Ahmed 22  If an included study examined students' and teachers' comfort and health, this is linked to the quality of teaching or learning.
Examined students' cognitive performance, for example, attention or concentration tests, and students' score on school tests, for example, calculation and reading tests, was classified as short-term academic performance. Students' grades of a course or academic year were classified as long-term academic performance. Reported statistical significant effects of different IEQ conditions on students comfort, health, and academic achievement were included in the analyses. In addition, reported statistical significant effects on students' academic achievement were quantified by calculating the increase or loss of the reported performance, based on the scores presented.  Table 1 presents the direct associations between indoor environmental conditions and students' academic performance. Table 2 presents direct associations between actual or perceived indoor environmental conditions and perceived academic performance, physical health, or comfort.

| RE SULTS
The results are presented on the basis of the RQ-score, beginning with the study with the highest score, and include the main findings of the influence of the IEQ on teachers' and students' health and comfort and students' academic performance. Appendix 4 provides additional details on these studies, including information about the age of participants, measured indoor environmental performance indicators, and studied outcomes. accuracy for memory tasks was observed at an air temperature of 23°C, compared to 20 and 25°C (P < 0.001).
Sarbu and Pacurar 26 analyzed students' concentrated and distributive attention test scores in relation to air temperature, relative humidity, and CO 2 concentration. Students' cognitive performance peaked at temperatures between 24 and 26°C, a relative humidity of approximately 60%, and a CO 2 level of approximately 500 ppm.
Although the sample size of this experiment was relatively small The heart rate of the students increased with 8% (P < 0.05) at the end of the cognitive activity at Day 3 compared to Day 1 and with 7% (P < 0.05) compared to Day 2. An air temperature of 23.3°C was associated with thermal neutral sensation.
Xiong et al 28 explored the impact of three indoor environmental parameters, that is, thermal, acoustic, and visual conditions, on learning efficiency in an environment-controlled university classroom. Five female and five male students were exposed to three different air temperatures, three different desk illuminance levels, and three different noise levels. Students' cognitive performance was measured for each condition with four different cognitive function tests. For the perception-oriented task, students scored highest at a temperature of 22°C, an illuminance level of 2200 lux, and a background noise level of 50 dBA. The scores of a memory-oriented task were the highest at 27°C, 300 lux, and 50 dBA. At 22°C, 300 lux, and 40 dBA students scored the highest for a problem-solving task. The final task, the attention-solving task, was performed the best at 17°C, 2200 lux, and 40 dBA. The memory-oriented task was the only experiment in which students' cognitive performance was affected by all three indoor environmental parameters (P < 0.05).
Analyses of the results showed that cognitive performance can decline with as much as 52%, when conditions were the worst. Table 3 presents an overview of the quantified combined effect, of an intervention IEQ condition compared with the optimal IEQ condition, on cognitive performance tasks.
Yan et al 29   Attention test  Perceived alertness, mood, and visual comfort The effect of exposure to blue-enriched white light with a color temperature of 6,500K at an illuminance level of 500 lux has a positive effect on the outcome compared to exposure to warm white light with a color temperature of 3,500 K at an illuminance level of 500 lux + *

Cortisol concentration in blood
No effect was observed on the outcome if participants were exposed to blue-enriched white light with a color temperature of 6,500K at an illuminance level of 500 lux compared to when they were exposed to warm white light with a color temperature of 3,500 K at an illuminance level of 500 lux -Examination scores On the second day, most students experienced thermal discomfort, the difference between Day 1 and Day 2 was significant (P < 0.0001). This difference in thermal discomfort on Day 2 led to a decline of cognitive functions short-term memory (−12%, P = 0.007) and verbal ability (−24%, P < 0.001). There was no decline of the cognitive function reasoning, on the contrary, there was an improvement of 1%, but this effect was not significant (P = 0.92). The researchers did not report any health risks, caused by the experienced thermal discomfort on Day 2. However, this discomfort on Day 2 was associated with a higher cardiac sympathetic modulation, as indicated by higher values of heart rate (+10%, P < 0.001), which may have adversely influenced the cognitive performance of the students. Hoque and Weil 33 examined the thermal environment, thermal comfort, and test scores of 409 students. The aim of this study was to quantify the relationship between the air temperature, humidity, air speed, and perceived comfort and students' test score, as an indicator of their short-term academic performance. The researchers found that students who felt thermal discomfort performed worse on tests than those with no thermal discomfort (P < 0.001). Table 4 presents a summary of the effect of thermal sensation on different tasks and academic test scores. Note: See footnote to Table 1 for the explanation of all variables and symbols used.

TA B L E 2 (Continued)
temperature of 30°C, and with 29% at a lower temperature of 16°C (P < 0.001).
(P < 0.05). Compared to the contribution of the thermal and lighting conditions and IAQ, which contribute similar to the overall perceived IEQ, the acoustic conditions were found to be a relatively sensitive contributor to the overall indoor environmental satisfaction with an almost twice as high coefficient value (P < 0.0001).

Castro-Martínez et al 42 indicated that noise levels have an im-
portant effect on the students' attention processes, and that specific changes, aimed at decreasing reverberation values in classrooms (with at least 0.7-0.9 seconds) affect positively the levels of attention and students' short-term academic performance. They found that the 141 students, who participated in this study, scored significantly better (P < 0.01) on mathematics (+59%), statistics (+18%), and attention (+14%) in a classroom with an average reverberation time of 1.2 seconds compared to students in a classroom with an average reverberation time of 2.0 seconds. Figure 4 presents the relation between the studied variables, presented in the included studies, and the quality of teaching, learning, and students' academic performance. First, we reflect on the influence of the IEQ on the quality of teaching. Secondly, we will discuss the influence of the IEQ on learning.

| D ISCUSS I ON
Finally, we will discuss the influence of the IEQ on students' academic achievement.

| The influence of the IEQ on the quality of teaching
As explained in the introduction, the quality of teaching is determined by the level of comfort, mental health, and physical health of teachers. Mendell and Heath 15 relate a poor IEQ to adverse health outcomes and discomfort, which can impair teaching effectiveness and instructional practices, 7 which in return affect students' academic achievement. 2 Two publications were identified which addressed the quality of teaching. Therefore, the evidence for the influence of the IEQ on teaching is limited and focusses on one parameter, that is, acoustic conditions. High noise levels in classrooms can cause heavy strain on female teachers' vocal cords and increase teachers' health risks. 40 However, the intelligibility of a teacher's voice is an essential element in the transfer of knowledge from teacher to student. This is supported by the findings of Castro-Martínez et al 42 that acoustics in classrooms could affect the ability of students to hear the teacher. In addition, this ability to hear decreases substantially when the distance between teacher and student increases. 44 According to Jonsdottir, 45 voice amplification can improve the intelligibility of a teacher's voice.
This researcher reported evidence that voice amplification can positively influence the perceived quality of teaching by teachers, reduce teachers' experienced voice fatigue, and improve student attention. Although this evidence indicates that the acoustic conditions influence the quality of teaching, the amount of evidence is limited to one IEQ parameter, and based on this evidence, the exact influence of all IEQ parameters on the quality of teaching cannot be determined or quantified.

| The influence of the IEQ on the quality of learning
The quality of learning, like the quality of teaching, is determined by the level of comfort, mental health, and physical health of students.
Mendell and Heath 15 relate a poor IEQ to adverse health outcomes, discomfort, and distraction of students; the latter negatively influencing students' achievement.
The actual and perceived IAQ can be positively influenced by applying a CO 2 demand-controlled ventilation system. 36 Sufficient ventilation will contribute to maintaining good air quality during the use of classrooms 36 and will positively influence the perceived overall IEQ. 41 One study could not find a relationship between the actual CO 2 concentration and perceived IAQ. 39 However, a significant correlation was observed between the actual thermal sensation of students and the perceived IAQ, indicating a mutual interdependence between the perceptions of these two indoor environmental parameters. 39 Thermal neutral sensation varies per individual 33 and depends also on many factors, for example, climate, cooling or heating season, adaptation period, and room temperature at home. When the thermal environment is assessed, there is evidence that indicates gender differences. Female students tend to feel cold more than male students. 24 influence their thermal sensation vote. 48 Even students' socio-economic and socio-cultural background will influence their thermal sensation vote. 49 This explains why students' thermal sensation will differ, even among students in the same classroom and in the Application of these different correlated color temperatures imitates the natural change of daylight during the day and therefore supports teachers' and students' circadian rhythm. 30 Application of a lighting system with a color temperature of 4000K in classrooms can also influence the ability to concentrate positively. 29 Although artificial lighting systems are necessary for creating optimal lighting conditions for facilitating in-class activities, students should be always provided with access to daylight in order to regulate students' circadian rhythm and level of stress hormones, that is, cortisol. 30 And according to Reid and Zee, 50 regulation of students' circadian rhythm is important because it influences students' alert state and cognitive performance.
Acoustic comfort is an important factor, which might play a dominant role in how the overall IEQ is perceived by students. 41 Creating acceptable acoustic conditions in classrooms is important. Poor acoustic conditions can affect students' ability to hear the teacher. 42  These effects can lead to sick leave, which in turn can affect students' achievement. 15

| The influence of the IEQ on students' academic achievement
The focus of all included studies, which examined the effect of IEQ on students' academic achievement, was on students' short-term academic performance. Therefore, the impact of the IEQ on students' long-term academic performance could not be determined yet. Further research is needed to determine the possible relation between the short-term and long-term academic performance of students.
Nine of the included IAQ-studies 22,23,26,[29][30][31]35,39,41  The cognitive performance of students can decline by as much as 13% (P < 0.001) when the CO 2 concentration increases from 600 to 1000 ppm. 22,23 However, this concentration of CO 2 still meets prevailing guidelines. 53 High CO 2 concentrations of 1800 ppm might affect cognitive performance with 24% (P < 0.001). 22,23 The influence of high CO 2 concentrations, as proxy for the IAQ, was higher on complex and memory-oriented than for vigilance tasks. However, the study of Ahmed et al 22,23 is the only study that quantified the effect of IAQ on cognitive performance and examined only female students. Because of these limitations, these results need to be validated with additional field research to confirm the impact and should explore possible gender differences.
Thermal discomfort, caused by high or low temperatures, affects students' cognitive performance. 22,23,31,33,34 Barbic et al 31 observed a decrease of as much as 24% when students experienced thermal discomfort due to high temperature. However, not all thermal discomfort sensations lead to a deterioration of cognitive performance, 27 and the effect is most likely task dependent. Thermal sensations "cool" and "slightly cool" can positively influence cognitive performance 28 ; thermal sensations "cold," "slightly warm," "warm," and "hot" can affect cognitive performance negatively. 27 The thermal sensation "hot" affects cognitive performance of vigilance tasks and memory and learning tasks more than the thermal sensation "cold." 22,23 Nevertheless, Bajc et al 35 concluded that students' shortterm academic performance is not just a function of PMV index; there is no simple relation in real conditions that can link this performance to the PMV index alone.
The color temperature and light intensity of artificial lighting can affect the cognitive performance of students. 28 This effect can be as much as 23% but this percentage is based on an average recognition rate of objects. 29 The effect of these conditions on other cognitive tasks of students is not revealed yet.
Two studies 28,42  were affected due to a combination of these conditions. The combined effect of air temperature and CO 2 seems to increase when air temperature and CO 2 concentration increases according to Ahmed et al 22,23 Other factors, besides temperature, such as stress, sleep deprivation and pre-existing disease or illness, among others, may play a role in health-related symptoms, such as headache and tiredness. 36 Individuals who are fatigued are also more likely to experience increased levels of psychological distress, acute health symptoms, and behavioral problems; these problems affect human performance. 22,23 It is well documented that the four individual IEQ parameters do affect the short-term performance of students. Combined effects of thermal conditions and IAQ were observed by Ahmed 22,23 among 499 female students. In addition, they controlled the lighting and acoustic conditions. However, they did not analyze the combined influence of these conditions. Xiong 28 analyzed the combined influence of three IEQ parameters, thermal and lighting conditions and IAQ. None of the studies analyzed the combined influence of all four indoor targeted environmental parameters. Therefore, the magnitude of the combined influence of these four IEQ parameters cannot be quantified yet.

| FUTURE RE S E ARCH
This systematic review revealed existing evidence about the influence of the IEQ on the quality of teaching, learning, and students' short-term academic performance. However, the influence of the IEQ on the quality of teaching could be further explored. Not only the influence of the IEQ on teachers' health, also the effect of the IEQ on the quality of instructional practices, teaching effectiveness, and the motivation of teachers should be explored. Although the short-term academic performance has been analyzed in different studies, the relation between the IEQ and the long-term academic performance of students was not revealed. Additional research is F I G U R E 4 Relation between the studied variables and the quality of teaching, learning, and academic performance needed to better understand this possible relation and to quantify the impact on students' academic achievement.
For analyzing the actual environmental conditions, different measuring equipment was used and one or more key performance indicators, to determine the IEQ, were applied. Additional research is needed to determine the key performance indicators of the IEQ and how these should be measured in a classroom; in order to (consistently) relate perceptions, health symptoms, and performance to the actual IEQ. Determining key performance indicators can also contribute to making future results more comparable.
Although various standardized tests are available for measuring short-term cognitive performance, few methods were identified for measuring the effect of the IEQ on physical health effects, emotional response, and long-term academic performance. New methods should be developed and could help to reveal the influence of the actual and experienced IEQ on teachers' and students' health, cognitive performance, emotion, and behavior. 9

| LIMITATI ON S AND S TRENG TH
During the review process, all studies were assessed on quality and reliability. Assessors were the authors of this review. Each assessor examined the exact same studies. The scores of all assessors were compared and discussed and resulted in minimal differences. In addition, this process led to adjustments and fine-tuning of the assessment procedure. This procedure was developed by the assessors and included all rubrics, as no other tool was applicable to this specific domain.
Therefore, this tool can only be applied when studies related to the IEQ need to be assessed for relevance and quality. Cultural or geographical differences between the studies were not analyzed. Therefore, the optimal conditions, as presented in the collected evidence, may not be applicable in every situation and are bound to the specific cultural and geographical cultural backgrounds. However, these conditions can be used as an indication for the development of optimal indoor environment conditions for teachers and students in a specific setting.

| CON CLUS ION
The primary goal of this systematic literature review was to provide an overview of how classroom indoor environmental conditions influence the quality of teaching and learning and students' academic achievement in higher education. Although a wide range of relevant evidence of high-quality research was identified, the amount of evidence which examined the effect of the IEQ on the quality of teaching is limited to only two studies on acoustics. These studies illuminate how high background noise levels affect students' ability to hear teachers' voice and increase teachers' health risks. Evidently, this is insufficient to determine the precise influence of all four IEQ parameters on teaching quality.
In this context, the first hypothesis-that the IEQ influences the quality of teaching-cannot be confirmed or rejected due to a lack of evidence. However, there is some evidence which suggests the negative impact of impaired acoustic conditions on teachers' health. The second hypothesis-that the IEQ influences the quality of learning-is confirmed. Sufficient evidence confirms that a poor IAQ, thermal, acoustic, and lighting conditions negatively influence the quality of learning due to discomfort and impaired mental and physical health of students. Moreover, optimal conditions contribute positively to the quality of learning through creating an environment in which students feel more alert and pay more attention to the information presented in the lecture. Studies showing that the IEQ influences students' academic achievement partially confirm the third hypothesis. On one side, the available evidence that specifies the influence of individual or combined indoor environmental conditions on students' short-term academic performance is sufficient to conclude that these conditions can either influence this performance positively or negatively. Optimal IEQ conditions, in which the students performed at their best, were task-dependent, with a preference for a relatively cool, bright, and quiet environment and in ambient air with low CO 2 concentrations.
However, on the other side, the hypothesized influence of all IEQ parameters on students' long-term academic performance cannot be confirmed due to a lack of evidence. Therefore, the overall influence of the IEQ on students' academic achievement cannot be fully determined yet.

ACK N OWLED G EM ENTS
This study is part of the research project: Understanding how indoor environmental conditions affect teaching quality, learning, and academic achievement in higher education. This project is funded by the for her contribution to the reference and database management.

CO N FLI C T O F I NTE R E S T
The authors declare no competing interests. writing -review and editing (supporting).

PE E R R E V I E W
The peer review history for this article is available at https://publo ns.com/publo n/10.1111/ina.12745.

A PPE N D I X 1
Overview of used keywords

A PPE N D I X 3
Assesment procedure for relevance and quality of study Air-conditioner set temperature at home Self-reported ability to focus related to thermal discomfort Self-reported ability to focus related to other symptoms than thermal discomfort Self-reported headache Self-reported fatigue CLO = clothing insulation value, RH i = indoor relative humidity, RH o = outdoor relative humidity, t a = air temperature, t db = dry bulb temperature, t f = floor temperature, t g = globe temperature, t mr = mean radiant temperature, t o = mean outdoor temperature, t op = operative temperature, t r = radiant temperature, t w = temperature of walls, t wb = wet-bulb temperature, v a = air velocity.Lighting performance indicators: