LED professional Review (LpR) - Articles

Resources | LpR Article | Research | Sustainability | Environment | Apr 27, 2018

Repro-Light - Looking for a Sustainable and Modular Luminaire Architecture

Repro-Light - Looking for a Sustainable and Modular Luminaire Architecture The Repro-light project aims to re-conceptualize the European lighting industry towards more sustainability and competitiveness in terms of production and time to market. This will be achieved through the implementation of modular luminaire architecture and a smart production scheme, demonstrated by the development of a reconfigurable customized LED luminaire designed to improve the customers’ health. Read more »

Resources | LpR Article | Research | Optics | Engineering | Apr 13, 2018

Optimization of Freeform Optics Using T-Splines in LED Illumination Design

Optimization of Freeform Optics Using T-Splines in LED Illumination Design Freeform optics is the game changer in the illumination industry in terms of its ability to redirect the light into the target area. Non-Uniform Rational B-splines, commonly known as NURBS are widely used to represent freeform curves and surfaces. There are certain optical systems where local modification of the surface is necessary during the design or optimization phase. In such cases, NURBS cannot offer such transformations. But a new mathematical representation called T-splines make this feasible. Though its potentiality is well described, this has not been implemented in any optimization routine so far. Annie Shalom Isaac, Jiayi Long and Cornelius Neumann from the Karlsruhe Institute of Technology demonstrate the advantage of the local refinement ability of T-splines by implementing it in the optimization routine and the results are evaluated. Results show that T-splines provide more uniform and homogenous light distribution as compared to NURBS at a faster convergence rate. This makes optical design or optimization using T-splines an intuitive approach for future freeform design tasks. Read more »

Resources | LpR Article | Environment | Mar 27, 2018

A World of LED Lights - The Cost of Waiting

A World of LED Lights - The Cost of Waiting Today, LEDs dominate the lighting domain. They are efficient and manufacturers understand how to implement them for different lighting applications. While energy efficiency is rather well understood, the impact of the adoption speed is rarely discussed is. Benoit Bataillou, guest author from Pi Lighting, will have a look at the environmental cost of LED production versus the significant energy savings that a full transition to LEDs would bring. In a fictive scenario, he assumes that a transition takes place in a heartbeat today and compares that with the usually supposed scenario of a full transition to LED lights in 2025. Read more »

Resources | LpR Article | Quality | Optics | Mar 13, 2018

Glare Reduction Made Easy

Glare Reduction Made Easy A pleasant lighting atmosphere due to low glare at the workstation is not only pleasant and performance-enhancing, but also legally required according to EU standard EN 12464-1. But what does “glaring” mean here? Dr. Claudius Noack, Technical Director at NORKA Leuchten, explains if luminaires with the same luminous flux are glaring to the same degree and if the same luminaires are glaring to the same degree at different workstations. He answers the questions of what a manufacturer does and if manufacturers are lying to themselves and therefore to their customers when providing information on the glare rating. Read more »

Resources | LpR Article | Technologies | Light Generation | Tunable White Light | Feb 28, 2018

A New Technology Is Changing the Tunable White Solutions

A New Technology Is Changing the Tunable White Solutions Tunable white LEDs are one key element of human centric lighting. Until today, different solutions are currently available but none of them is easy to apply or cost effective enough to speed up the diffusion of human centric lights in building projects. A new approach for tunable white solutions is able to provide flexible lighting for multiple occasions without sacrificing output or going over project budget. Phil Lee, Senior Lighting Engineer from Meteor Lighting will compare this new technology, called ColorFlip™, to conventional tunable white solutions, and talk about current tunable white issues. Read more »

Resources | LpR Article | Tech-Talks Bregenz | Quantum Dots | Feb 27, 2018

Tech-Talks BREGENZ - Ken T. Shimizu, Research & Development Director, Lumileds

Tech-Talks BREGENZ - Ken T. Shimizu, Research & Development Director, Lumileds QDs have been a hot topic in lighting for a while already, but up until now they haven’t been adopted on a large scale in lighting. The adoption began in display devices because some of the technical issues were of less concern in this application. With continuing development, QDs are now also becoming interesting for general lighting applications. Ken Shimizu, Director of Novel Technologies and Devices, Research and Development at Lumileds, attended the LpS in Bregenz and made a presentation about the company’s QD technology. In this interview he gives some background information about the QD program and future steps. Read more »

Resources | LpR Article | Commentary | Trends | Feb 21, 2018

Can You Show Me the Next S-Curve, Please?

Can You Show Me the Next S-Curve, Please? The evolution of technologies is often described using the “S-curve” model. In the early stage, in the first phase of its life cycle, technology is mainly driven by fundamental research. Only a few players are active at that time and innovation steps are quite large. In the second phase, early adopters start to develop products and bring them to market. This phase is characterized by huge investments. In the third phase, more and more players enter the technology field, competition becomes important and development speed of the technology decreases. In the last phase, the technology is mature, (nearly) everybody can use it, there are fewer margins and the technology should be replaced by a new one. Many of the SSL technologies have meanwhile reached maturity. Where are the upcoming technologies, what will be the next S-curve? Looking at technology discussions and lectures at LpS 2017 I tried to find answers to these questions. Read more »

Resources | LpR Article | Technologies | LiFi | Jan 15, 2018

LiFi - What It Is, How It Works, What It Provides, How to Apply, and Its Future Prospects

LiFi - What It Is, How It Works, What It Provides, How to Apply, and Its Future Prospects The acronym LiFi (Light Fidelity) was born at the beginning of the 2010s. Its name derives from the very well-known WiFi (Wireless Fidelity). The term VLC (Visible Light Communication) is used in the restricted instances of visible light. Mr. Luc Chassage who works for Oledcomm and the Versailles University is also Scientific Committee President of the Global LiFi Congress that offers 20 lectures dealing with all aspects of LiFi. He is a profound expert in this technology field. Mr. Chassage explains the functionality, pitfalls and hurdles to overcome, the disadvantages and advantages, and best practice to apply LiFi. Read more »

Resources | LpR Article | Research | Thermal Management | Jan 15, 2018

Thermal Issues Posed by Compact Packaging and IoT for Next Generation SSL

Thermal Issues Posed by Compact Packaging and IoT for Next Generation SSL Besides general lighting, LEDs are penetrating many areas. At the same time, Internet of Things (IoT) has been rapidly evolving. Added electronics are expected to add an additional 70% to overall heat generation. Therefore, solving thermal problems will become more important again; on a par with footprint area and cost. Prof. Mehmet Arik, Director of EVATEG Center for Energy Efficient Electronics and Lighting Technologies at the Ozyegin University, and Umut Zeynep Uras, master student at the Ozyegin University, present some of the current, local, hotspot thermal issues caused by tight packaging. The severity of the problem for future lighting systems with added IoT will also be discussed. Finally, possible technologies to meet those challenges will be shown. Read more »

Resources | LpR Article | Research | Light Generation | Jan 01, 2018

Hybrid Quantum Dot Light Emitting Electrochemical Cells

Hybrid Quantum Dot Light Emitting Electrochemical Cells Several new light generation technologies that are overshadowed by LEDs and OLEDs are investigated. Most of these technologies are in a very early stage of research. One such technology, the LEC technology, was presented at LpS 2017. Light emitting electrochemical cells can be compared to OLEDs, but they are based on a much simpler inorganic architecture. The innovation in the presented approach lies in the combination with quantum dots, resulting in a hybrid solution. This novel attempt with all its consequences and future prospects was the reason that the LpS Scientific Award jury voted to bestow the award on Dr. Ekaterina Nannen, Group Leader of the Research Group „Solid State Lighting“ at the Nano-Energie-Technik- Zentrum (NETZ) of the University Duisburg-Essen and her research team, Julia Frohleiks and Svenja Wepfer. Read more »

Resources | LpR Article | Research News | CIE | Quality | Jan 01, 2018

Color Reproduction and Measurement of 3D Objects

Color Reproduction and Measurement of 3D Objects CIE Division 8 Image Technology is responsible for the study of the optical, visual and metrological aspects of the communication, processing, and reproduction of images, using all types of analogue and digital imaging devices, storage media, and imaging media. The Division is continually working on recommendations to improve color image reproduction techniques, including, for example, colorappearance models, color-difference evaluation and gamut-mapping algorithms. Current technology is able to transform color images from one digital medium to another, under various viewing conditions, while maintaining the appearance of each color in the image. This process has been applied in the graphic arts industry with great success. According to Kaida Xiao, Chair of CIE's Division 8 TC 8-17, the CIE standard observer and psychophysical data for color-appearance and color-difference modelling were developed using flat, 2D color samples. He explains that to meet the increasing requirements for color image reproduction for 3D objects, new research and recommendations are highly desired. Read more »

Resources | LpR Article | Automotive | Driver IC | Controls | Dec 28, 2017

Interior Automotive Lighting Control Redefined

Interior Automotive Lighting Control Redefined In modern car’s interior lighting, tough requirements and rising complexity are a huge challenge. A new industry consortium was formed to meet this technological challenge and to provide a comprehensive ecosystem for the new digital LED lighting paradigm. The founding members of the Open ISELED Alliance are Inova Semiconductors (ISELED "Digital LED" concept and LED controller), Dominant Opto Technologies (LED manufacturing and packaging), NXP (system microcontroller), TE Connectivity (system integration and connection technology) and Pforzheim University (theoretical framework). The alliance recently added LucieLabs (software, firmware), a French IoT Software startup to its line-up. The goal of all these organizations is to work in close cooperation to present a complete system solution - a true ecosystem. Roland Neumann, CTO of Inova Semiconductors introduces the challenges and the worked out innovative solution that uses a single system controller to individually address up to 4,096 LEDs. Read more »

Resources | LpR Article | Event-Reports | Technologies | Trends | Dec 13, 2017

LpS Gets a Younger Sibling to Foster a Holistic System Approach

LpS Gets a Younger Sibling to Foster a Holistic System Approach For the most part our readers are aware of the fact that the LpS has a strong focus on the component level, but after the 6th event, the Luger Research team realized that it was time to find a way to push the more holistic system approach. After much consideration and careful planning, the Trends in Lighting (TiL) Forum and Show was initiated and took place in conjunction with the LpS 2017. Arno Grabher-Meyer, Editor-in-Chief at LED professional took a close look at both exhibitions and the lectures to find out what the audience thought of the extension and broader outlook. Read more »

Resources | LpR Article | Quality | Measurement | Calibration | Dec 11, 2017

Avoiding Brightness and Color Mismatch with Proper RGB Gamut Calibration

Avoiding Brightness and Color Mismatch with Proper RGB Gamut Calibration For well over a decade, proponents of Solid-State Lighting (SSL) have been offering bullish forecasts concerning the adoption of LEDs for general and specialized lighting applications. Recent years have seen those rosy predictions come true, with LED lighting now almost completely dominating the market for new construction, retrofit, and many replacement lighting applications. For many of these applications accurate color calibration is required. Rood Bouten, CTO at Admesy, explains the reasons and how to perform a proper RGB gamut calibration. Read more »

Resources | LpR Article | Commentary | Test Equipment | Dec 11, 2017

The Value of High-End Labs for High Quality Lighting

The Value of High-End Labs for High Quality Lighting With the relocation to the Augsburg site in 2015, the Osram laboratory equipment includes a number of integrating spheres of different sizes up to 3 meters in diameter, several goniophotometers A/B/C types, a rotary mirror light distribution meter and a hemispherical goniometer with a measurement radius of 2.65 meters, optical bench measuring systems with up to 35 meter measuring distance, corresponding high-quality photometric receivers and spectral radiometers as well as the necessary components for the electrical operation of lamps - according to customer or standardized specifications. Read more »

Technologies | Resources | Smart Lighting + IoT | Electronics | LpR Article | Nov 30, 2017

SoC Technologies in Lighting - Today’s Landscape and Tomorrow's Practices

SoC Technologies in Lighting - Today’s Landscape and Tomorrow's Practices A system-on-chip (SoC) quite suddenly became an important component in the lighting industry, fueling IoT innovation and opening new opportunities, while at the same time bringing disruption and new challenges. With rapid advancements in wireless communication, the impact of connected technologies on the lighting business will only keep increasing. This means deeper integration with SoCs and more attention from silicon vendors as they start competing for market share in this promising segment. But what is the current state of SoC design from the lighting perspective? Are chipmakers keeping up with the growing expectations for wireless lighting control solutions that are mature and truly reliable? When developing its complete Bluetooth software stack for professional lighting, Silvair worked with a number of different SoCs. Therefore, Piotr Winiarczyk, Wireless Solution Architect, and Szymon Rzadkosz might have found the answers to these questions. Read more »

Resources | LpR Article | Technologies | Electronics | Drivers | Nov 09, 2017

LED Driver Miniaturization - Opening New Opportunities for Solid State Lighting

LED Driver Miniaturization - Opening New Opportunities for Solid State Lighting While LEDs have significantly improved over the past decade, driver technologies have not kept pace and are, in some respects, the limiting factors for new applications. Size is a particular issue. Dramatically increasing the switching frequency helps to reduce size but often causes other issues or is costly. Mickey Madsen, CEO of Nordic Power Converters, explains how his company has overcome the hurdles and made it feasible by designing very high frequency LED drivers. Read more »

Resources | LpR Article | Research | Electronics | Drivers | Nov 02, 2017

LED-Retrofit Based on AlGaN/GaN-on-Si Field- Effect Transistor Drivers

LED-Retrofit Based on AlGaN/GaN-on-Si Field- Effect Transistor Drivers Efficient driver technologies for LED systems are still a relevant topic. Several new approaches are proposed and new technologies are under development. Andreas Zibold, PhD student at the Fraunhofer Institute for Applied Solid State Physics IAF, and his co-authors, M. Kunzer, R. Reiner, B. Weiß, P. Waltereit, R. Quay, J. Wagner, and O. Ambacher demonstrate the suitability of AlGaN/GaNon- Si field effect transistors (FETs) for their use in LED drivers. The transistors are tested in an isolated buck converter and an efficiency of 86% is measured for the full converter circuit. The driver circuit is combined with an LED module based on a laser-structured Aluminum Nitride (AlN) ceramic board onto which 21 high power white-emitting LED chips are mounted. This combination resulted in an LEDRetrofit lamp with a total light output of 2676 lm at an efficacy level of 119 lm/W. The results compare favorably to state-of-the-art commercial solutions. Read more »

Resources | LpR Article | Interview | Trends | Horticulture | Sep 25, 2017

Trends in Horticulture Lighting

Trends in Horticulture Lighting Cree has been a leader in general lighting applications for over 20 years and has customers ranging from restaurant chains to global government agencies. Paul Scheidt began his career in Cree in 2005, working on the development of their lighting applications. During this time, he has seen an increase in the horticulture lighting application. LED professional spoke to Paul Scheidt about horticulture lighting and what he thinks is behind this recent trend. He also shares his views of what he thinks the future holds for both Cree and horticulture lighting applications. Read more »

Resources | LpR Article | Quality | Perception | Sep 25, 2017

Lighting to Achieve Optimal Appearance

Lighting to Achieve Optimal Appearance Visual appearance of an object or space depends on the characteristics of the lighting applied. The objective definition of light quality often doesn’t tell the whole story. Light intensity, its spectral composition and distribution in space, as well as individual preference, must be considered. Nevertheless, aiming for the absolute optimum is only recommended when private rooms are concerned. As visual appearance is key in driving consumer demand, it is important to tune the light to maximize effectiveness and visual pleasure for most consumers. Markus Reisinger, owner and CEO of the Lighting Research Studio, discusses this complex situation with examples. Read more »

Resources | LpR Article | Measurement | Special Applications | UV | Sep 25, 2017

Issue 63 | Challenges in UV Measurement

Issue 63 | Challenges in UV Measurement Over the past decade UV LEDs have emerged as a highly attractive alternative to conventional UV emission sources. They are cost effective and energy efficient devices in a small housing. These advantages allow new fields of applications and access to a larger group of users - even in the consumer market, e.g. water purification. Dr. Tobias Roesener, Product Manager at Instrument Systems, explains what makes accurate measurement of UV LEDs so complicated and what the crucial requirements on the measurement equipment are. In addition, he discusses calibration and stray light issues. Read more »

Resources | LpR Article | Technologies | Light Conversion | Quantum Dots | Sep 25, 2017

Quantum Dot Based White LEDs for General Illumination

Quantum Dot Based White LEDs for General Illumination Colloidal quantum dot based white LEDs can be integrated into commercial products meeting the stringent reliability requirements for general illumination and providing LED efficiency gains of 5% to 15% over commercial phosphor based LEDs at CCT’s ranging from 5000 K to 2700 K. Unlike earlier demonstrations, the QD material is applied in an on-chip configuration resulting in drop-in fit, form, and function compatibility to existing LED based luminaires and lamps. Ken T. Shimizu, Director, Novel Technologies and Devices, Research and Development, M. Böhmer, D. Estrada, S. Gangwal, S. Grabowski, H. Bechtel, E. Kang, K. J. Vampola, D. Chamberlin, O. B. Shchekin, and J. Bhardwaj from Lumileds showcase the advantages of on-chip QD LEDs: A commercial lamp at 3000K color temperature and 90 CRI is substituted with QD based LEDs resulting in a system level efficiency gain up to 17%, attributed to the reduced blue LED droop from the lower drive current and the lower heat sink temperature when compared to the standard phosphor based LED lamp output. Read more »

Resources | LpR Article | Research | Medical | Sep 25, 2017

Challenges when Designing LED-Based Illumination Systems in Medical Applications and Diagnostics

Challenges when Designing LED-Based Illumination Systems in Medical Applications and Diagnostics LEDs have become indispensable in medical technology and dentistry. But the requirements placed on these lighting products are very high: Minimized size, high, application specific color rendering index, efficient temperature management, usability and excellent disinfection opportunities are all extremely important. Prof. Paola Belloni from the Steinbeis Transfer Center Illumination Optics and Lighting Engineering and Furtwangen University, and Alexander Gärtner from the Faculty of Mechanical and Medical Engineering of the Furtwangen University discuss the requirements for different applications such as endoscopy, surgeries, dental devices, and photodynamic therapy. Further topics are the development of a self-disinfecting operation interface with edge-lit UV-A LEDs, and a new optimization approach, taking into account the reflection and absorption properties of human tissues. Read more »

Resources | LpR Article | Research | Measurement | Lighting Simulation | Optics | Sep 25, 2017

Measurement of Angular and Spatial Resolved Spectral Rayfiles

Measurement of Angular and Spatial Resolved Spectral Rayfiles The enhanced complexity of modern lighting systems has increased the importance of realistic light source models during the optical design process of LED-based luminaires. I. Rotscholl, Research Associate, K. Trampert, C. Neumann, I. Leopoldo Sayanca from the Karlsruhe Institute of Technology, U. Krüger and F. Schmidt from the TechnoTeam Bildverarbeitung GmbH, propose a method to enhance the often used LED light source model “rayfile” towards a “spectral rayfile”. A spectral rayfile would be a model that associates each ray with its own spectrum and therefore describes varying spectra as a function of angular direction and spatial starting position. The PMBS (physical motivated basis spectra) method is based on the assumption that each LED spectrum consists of a weighted sum of individual basis spectra, for instance those of individual semiconductors and phosphors. There is no need for any special measurement equipment but a classic nearfield goniophotometer and some off-the-shelf optical filters. This method requires at least one spectral measurement and just a minimum of goniophotometric measurements with different optical filters. Finally, the authors demonstrate the potential of this method by applying the concept on a typical LED and compare the results to the often used Blue/Yellow approach in terms of accuracy and applicability. Read more »

Resources | LpR Article | Tech-Talks Bregenz | Quality | Human Centric Lighting | Optics | Sep 25, 2017

Tech-Talks BREGENZ - Dr. Wilfried Pohl, Research Director, Bartenbach GmbH

Tech-Talks BREGENZ - Dr. Wilfried Pohl, Research Director, Bartenbach GmbH Bartenbach is one of the pioneers in light planning and lighting research. Since Christian Bartenbach Senior founded the engineering office in 1976, the company has been dedicated to light and visual perception. Several lighting inventions made over the years, can be attributed to Bartenbach. Dr. Wilfried Pohl, as a member of the Managing Board and Director of Research at Bartenbach GmbH, has played a substantial role in many developments. LED professional talked with him about Bartenbach’s history, education in the lighting business, the lighting parameters he deems very important, the quality of light, "Human Centric Lighting" and "Biodynamic Lighting“, and how LEDs have changed the light planning and lighting research company, in general. Read more »

Resources | LpR Article | Research News | CIE | Health | Sep 25, 2017

CIE Calls for Focused Research Efforts to Support Healthful Lighting Recommendations

CIE Calls for Focused Research Efforts to Support Healthful Lighting Recommendations Not so long ago, vision scientists thought that light detection - photoreception - was exclusively performed by rod and cone cells in the retina. Photobiologists, however, conclusively demonstrated otherwise with the identification of the intrinsically photoreceptive retinal ganglion cells (ipRGCs) [1]. Whereas rods and cones detect pattern and color, and send this information to the visual cortex, ipRGCs (of which we are learning there are several subtypes) detect irradiance, and route their information to many brain structures. The most thoroughly studied of these is the suprachiasmatic nucleus of the hypothalamus, location of the central circadian clock, where the light and dark signals trigger the offset and onset of production of the hormone melatonin. As shown in figure 1, however, ipRGCs also project to other structures, about which, as yet, we have little information. Read more »

Resources | LpR Article | Commentary | Business | Sustainability | Sep 21, 2017

Lighting Delivering Increased Value To Society - A Strategy For Growth

Lighting Delivering Increased Value To Society - A Strategy For Growth In recent years we have seen energy efficiency as the key driver for regulation as well as growth. Thanks to the arrival of LEDs the industry is already providing energy savings greater than any other sector. As the LED revolution rapidly continues, where next for the EU lighting industry? LightingEurope, the European industry association for the lighting industry has developed a strategy for growth which aims to fundamentally deliver value to society while aligning with the need to move towards a circular economy. Read more »

Resources | LpR Article | Quality | Applications | Sep 14, 2017

Technology Challenges in Professional Tunnel Lighting Applications

Technology Challenges in Professional Tunnel Lighting Applications The guide for tunnel lighting CIE 088:2004 is the most established international standard for the illumination of road tunnels. However, Switzerland’s ASTRA (Bundesamt für Strassen) and the ASFINAG in Austria both provide guidelines that go well beyond these requirements. Maximilian Herzig, Product and Key Account Manager Lighting at SWAREFLEX GmbH shows solutions to satisfy these requirements and explains why the commonly used value of "lumen per watt" is not a perfect method of evaluating system performance and efficiency. Read more »

Resources | LpR Article | Research News | CIE | Measurement | Calibration | Sep 13, 2017

CIE Research Strategy on Defining New Calibration Sources and Illuminants

CIE Research Strategy on Defining New Calibration Sources and Illuminants In photometry and radiometry, traceability of measurements requires appropriate calibration sources and transfer detectors. A major challenge is the technological revolution of lighting products towards LED lighting and the ban of incandescent lamps. This raises concern about the availability of incandescent photometric standard lamps in the future while the prices of such standard lamps are already increasing. In addition, calibration conditions should ideally be chosen to be as close as possible to the measurement conditions. Furthermore, the number of LED lighting measurements in laboratories and in the field has significantly increased, while the calibration of photometers is still done using incandescentbased standards. Therefore, it is important to investigate the pros and cons of replacement of conventional standard lamps with new solid-state technology. Peter Blattner and Tony Bergen, Division 2 Director and Secretary respectively, explain how CIE has defined the research topic “New Calibration Sources and Illuminants for Photometry, Colorimetry, and Radiometry” to address these concerns. Read more »

Resources | LpR Article | Commentary | Technologies | Trends | Sep 13, 2017

Brave New World and the Dualism of Light(ing)

Brave New World and the Dualism of Light(ing) The lighting business has been quite predictable over a long period of time. Technical changes were introduced slowly, dominated by a handful of leading companies, and mostly due to new, but not disruptive light sources. The life of engineers was mainly determined by a manageable number of parameters: Lighting requirements, light source parameters, costs, product dimensions, and the odd, required feature. Read more »


UniDriver® Universal Input Line Voltage LED Drivers

UniDriver® Universal Input Line Voltage LED Drivers LTF Technology’s UniDriver Series offers the ultimate in flexibility and ease of driver selection for lighting industry OEMs and specifiers. These technologically-advanced LED drivers offer True-Tri-Mode dimming from 100V to 277V (ELV, TRIAC, 0-10V), dimming levels from 100% to 0.1%, compatibility ... Read more »


NICHIA LED Technology Presented at LICHTWOCHE München

NICHIA LED Technology Presented at LICHTWOCHE München LED manufacturer NICHIA, a specialist in highly efficient lighting, Human Centric Lighting and the imitation of natural light, will participate in the Munich Lichtwoche 2021 from 5 to 12 November with a light installation, two presentations and a discussion on the topic of UV-C. The light ... Read more »