Initial Benchmarks of UV LEDs and Comparisons with White LEDs

Abstract

Light-emitting diodes (LEDs) can emit radiation that spans the range from near infrared (IR) to all three bands of ultraviolet (UV) radiation (i.e., UV-A, UV-B, UV-C). These emission sources are fabricated by varying doping levels of the aluminum gallium indium nitride (AlGaInN) alloy system, which tunes the emission wavelength of the semiconductor. During the past 20 years, the blue LED, made from InGaN, has advanced technologically to the point that it now provides the backbone for the solid-state lighting revolution that is occurring in general illumination. With proper doping, the InGaN alloy system can be extended to UV-A emission wavelengths as low as 362 nanometers (nm); however, producing LEDs that emit in the UV-B and UV-C bands requires the use of AlGaN alloys. Unfortunately, AlGaN semiconductors are not at the same level of technological development as InGaN, and LEDs made from AlGaN suffer from a variety of inefficiencies arising from electrical and optical limitations of the current technology. This report is aimed at benchmarking the performance of UV LEDs across all three bands in an effort to understand the current state of the technology.UV sources have many industrial applications, and their total market exceeds $750 million. Examples of applications for UV sources include ink and polymer curing (primarily UV-A sources), medical treatments (primarily UV-B sources), and disinfection (primarily UV-C sources). While UV-A applications are the largest market today, the increased need for surface and air disinfection is expected to create a significant market opportunity for UV-C sources in the near future. The current technology most widely used for UV sources in all three bands is the mercury discharge lamp, which has moderate energy efficiency but also has a number of limitations including compatibility with compact form factors, long-term reliability, and end-oflife issues associated with disposing a glass tube containing mercury without creating environmental contamination. UV LEDs have the potential to displace mercury lamps in UV applications in much the same way that white LEDs have displaced fluorescent lamps in many commercial and residential lighting markets.The primary goal of this report is to benchmark the initial level of performance of a selection of commercial UV LEDs across all three bands (i.e., UV-A, UV-B, UV-C). To provide the initial performance benchmarks, a test matrix containing 13 different UV LED products was created in association with the LED Systems Reliability Consortium (LSRC). The products in this test matrix were all commercially available as of June 2021, and at least 22 samples of each product were tested. In addition, two common, commercial white LEDs were tested to provide a benchmark against blue-pumped white LEDs. Testing of the samples included electrical performance testing (e.g., current-voltage measurements) and photometric testing in a calibrated integrating sphere capable of measuring devices in the UV-A, UV-B, and UV-C bands. The electrical testing provid...

Operating Lifetime Study of Ultraviolet (UV) Light-Emitting Diode (LED) Products

“…The most common source of UV radiation is the low-pressure mercury vapor (LPMV) lamp, which offers high efficiency (30-40%), is low cost, and has been used for many years in the field [1,4]. Although these LPMV lamps are relatively efficient, they have many known limitations, including lamp breakage, causing mercury to leak into the environment [5]; tendency to produce ozone; limited form factors; and low luminaire efficiency [4].…”

“…UV LEDs have the potential to eliminate some of the limitations of LPMV lamps (e.g., LEDs are amenable to many form factors, and lamp breakage does not release harmful substances into the environment). However, UV-B and UV-C LED sources currently have significantly lower source efficiencies (1-5%) than LPMV lamps [1]. The inefficiency could be counterbalanced to some degree by their directional emission profile.…”

“…Improving the energy efficiency of UV LEDs involves addressing key technical challenges in the development roadmap that broadly fall into electrical and optical technology needs [1,4,[6][7][8][9][10][11].…”

“…Because the bandgap of gallium nitride (GaN) corresponds to an emission wavelength of 362 nm, UV-A LEDs can be made by doping indium (In) into GaN to create indium gallium nitride (InGaN) alloys [1,4,[6][7][8][9][10][11]. This same materials system, albeit at higher In doping levels, is also used to make blue LEDs that are widely applied as sources in solid-state lighting (SSL) devices.…”

“…However, before emerging UV LED technologies can displace LPMV lamps, the efficiency and reliability of these sources must meet the user's expectations in each application. An earlier report focused on the construction and initial performance of commercial UV LED products in radiometric and current-voltage (I-V) tests [1]. This report focuses on the long-term performance and reliability of the same set of commercial products.…”