Citation: Naskari, V.; Doumenis, G.; Masklavanos, I. Irradiance Non-Uniformity in LED Light Simulators. Information 2023, 14, 316. https://doi.org/10.3390/ info14060316 Academic Editor: Zahir M. Hussain Received: 6 April 2023 Revised: 26 May 2023 Accepted: 26 May 2023 Published: 30 May 2023 Copyright: © 2023 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/). information Article Irradiance Non-Uniformity in LED Light Simulators Vasiliki Naskari *, Gregory Doumenis and Ioannis Masklavanos Department of Informatics and Telecommunications, University of Ioannina, GR47100 Arta, Greece; greg@uoi.gr (G.D.); i.masklavanos@uoi.gr (I.M.) * Correspondence: naskvasil@uoi.gr Abstract: Photovoltaic (PV) cells are a technology of choice for providing power to self-sufficient Internet of Things (IoT) devices. These devices’ declining power demands can now be met even in indoor environments with low light intensity. Correspondingly, light simulation systems need to cover a wide spectrum of irradiance intensity to emulate a PV cell’s working conditions while meeting cost targets. In this paper, we propose a method for calculating the irradiance distribution for a given number and position of LED sources to meet irradiance and uniformity requirements in LED-based light simulators. In addition, we establish design guidelines for minimizing non-uniformity under specific constraints and utilize a function to evaluate the degree of non-uniformity and determine the optimal distance from the illuminated surface. We demonstrate that even with a small number of low-cost LED sources, high levels of irradiance can be achieved with bounded non-uniformities. The presented guidelines serve as a resource for designing tailored, low-cost light simulators that meet users’ area/intensity/uniformity specifications. Keywords: irradiance; non-uniformity; indoor PV cells; light-emitting diode; light simulator 1. Introduction The rapid expansion of industrialization, coupled with population growth and an increase in energy consumption per capita, has resulted in a surge in energy demand across the globe. However, the use of fossil fuels for energy production has reached saturation levels due to escalating environmental concerns and resource depletion [1]. To address this challenge, the focus has turned toward more economical, cost-effective, and environmentally friendly energy solutions, with renewable energy sources (RESs) being the most promising solution to meet the growing energy demand [2]. At the same time, the Internet of Things (IoT) has become an integral part of modern society, enabling the connectivity of physical devices through the internet and introducing new forms of communication between people and things, as well as between things themselves [3]. Through the exchange of data for remote monitoring and controlling devices, the IoT has become an essential technology in daily life around the world [4–6]. Solar energy is a clean and renewable source of energy, which makes it an attractive option for powering IoT nodes, especially those located in remote or inaccessible areas where it is difficult or expensive to run power lines. Solar-powered IoT nodes can be used for various applications, such as environmental monitoring, smart agriculture, and industrial automation, among others. Furthermore, advancements in solar technology have enabled the use of solar power to provide energy to small, low-power devices that consume very little energy, such as sensors and actuators. These devices can collect data and perform automated actions without the need for human intervention, thereby improving the efficiency and sustainability of energy consumption and reducing the overall carbon footprint of IoT networks [7,8]. Photovoltaic cells have been extensively studied and have resulted in high conversion efficiencies of up to 20% in optimal weather conditions [8]. However, research on the performance of photovoltaic cells under indoor lighting conditions is much less efficient Information 2023, 14, 316. https://doi.org/10.3390/info14060316 https://www.mdpi.com/journal/information