Citation: Králiková, R.; Džu ˇ nová, L.; Lumnitzer, E.; Piˇ nosová, M. Simulation of Artificial Lighting Using Leading Software to Evaluate Lighting Conditions in the Absence of Daylight in a University Classroom. Sustainability 2022, 14, 11493. https://doi.org/10.3390/ su141811493 Academic Editor: Antonio Peña-García Received: 24 June 2022 Accepted: 12 September 2022 Published: 14 September 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sustainability Article Simulation of Artificial Lighting Using Leading Software to Evaluate Lighting Conditions in the Absence of Daylight in a University Classroom Ružena Králiková, Laura Džu ˇ nová *, Ervin Lumnitzer and Miriama Pi ˇ nosová Department of Process and Environmental Engineering, Technical University of Kosice, 040 01 Kosice, Slovakia * Correspondence: laura.dzunova@tuke.sk Abstract: This paper focuses on evaluating lighting conditions in a university classroom used for day and evening classes. The evaluation was made with regard to the legislation requirements for evening classes and adult education. The practical part of this paper consists of illumination measuring and simulation. A RadioLux 111 luxmeter was used to measure the illumination during the absence of daylight, which often occurs, especially in winter during the later hours. The simulation was performed in the DIALux EVO 10.1 and ReluxDesktop lighting design software. In both software, a 3D model of the classroom was created to represent its actual state. The results of the measurement and both simulations were compared with each other and with the requirements of the legislation. The requirements for evening classes have not been met in all three cases; therefore, the lighting simulation tools were used to improve the lighting system design concerning its energy efficiency and costs. This paper points out the benefits of using freely available computer software in the process of the calculation and improvement of lighting systems. Keywords: lighting design software; DIALux; Relux; lighting evaluation 1. Introduction Light is an integral part of our lives, but with the evolution of artificial lighting, the human lifestyle has begun to change. Thanks to artificial lighting, people increasingly stay up into the night and have an irregular sleep–wake cycle, which leads to the disruption of the circadian rhythm. As we spend more and more time indoors, whether at work, school, or leisure, we are exposed to artificial lighting during the night and the day. Therefore, the topic of suitable lighting conditions in buildings is gaining importance. Unsuitable lighting conditions make it difficult to perceive the surroundings, and can cause headaches, eyestrain, or other health problems. Both natural and artificial lighting affect a person’s biological clock and hormonal system, and, therefore, affect their overall health. In terms of artificial lighting, cooler blue light and higher illuminance improve the ability to concentrate and stay alert [1,2]. Blue light forms the predominant part of natural light and plays an important role in suppressing melatonin production, but it is also produced in light-emitting diodes (lights, monitors, screens). Most modern LED devices and luminaires are designed so that they emit warmer colors with minimum blue spikes. Continuous suppression of melatonin production can lead to various health problems, so evening exposure to blue light should be minimized. On the contrary, low illuminance leads to melatonin secretion. Melatonin, often referred to as the sleep hormone, reduces alertness and concentration, and prepares the body for sleep. The disruption of circadian time, e.g., by exposure to artificial lighting in the evening, has been associated with many health consequences, including metabolic and cardiovascular diseases, psychiatric disorders, cancer, or even increased mortality [3]. The negative side effects of disturbing the circadian rhythm by artificial lighting can be mitigated by optimizing the lighting system. Several studies have addressed the impact Sustainability 2022, 14, 11493. https://doi.org/10.3390/su141811493 https://www.mdpi.com/journal/sustainability