An Introduction to UV-C LEDs

What is UV-C?

“UV-C” refers to the portion of the electromagnetic spectrum spanning wavelengths from 100 to 280 nm (according to the ISO-21348 standard) or the narrower range from 200 to 280 nm (according to common practice). These wavelength ranges place UV-C within the ultraviolet (UV) portion of the electromagnetic spectrum, referred to here as the “UV radiation spectrum.”

Discovered by physicist Johann Wilhelm Ritter at the start of the 19th century, UV radiation spans the wavelengths from 10 nm to 400 nm, occupying the range between visible light and X-rays.

UV radiation spectrum

The ISO-21348 standard divides the UV radiation spectrum into three sub-ranges:

    1. UV-A (315 – 400 nm), sometimes known as ‘black’ light;
    2. UV-B (280 – 315 nm), which is responsible for both sunburn and for helping the human body generate vitamin D; and,
    3. UV-C (100 – 280 nm or 200 – 280 nm), also known as deep UV, UVC or germicidal UV, which has applications in sterilization and sensing.

The spectrum emitted by the sun does contain ultraviolet light including UV-A, UV-B, and UV-C, but the ozone layer in earth’s atmosphere absorbs 97% to 99% of the ultraviolet light. Thus, only UV-A and a small portion of UV-B reaches the earth’s surface.

What are the Germicidal Benefits of UV-C?

With a sufficient dose, UV-C radiation can inactivate any micro-organism, including viruses, bacteria, fungi and protozoa, making it a universal germicide. UV-C radiation achieves this outcome by two primary mechanisms, depending on the wavelength of the radiation.

    1. UV-C radiation between approximately 230 nm and 280 nm damages nucleic acids (DNA and RNA).
    2. UV-C radiation between approximately 200 nm and 250 nm damages proteins.

The UV-C induced damage to micro-organisms prevents them from replicating, which prevents them from causing or spreading infection.

UV-C radiation has well-known germicidal properties

The ability of UV light to act as a ‘mutagen’ at a cellular level has been known for many years. This property was first described in an 1878 scientific paper, while Niels Finsen won the 1903 Nobel Prize for Medicine for his work with UV on the treatment of tuberculosis of the skin.

Where is Deep UV Used?

Because of its germicidal properties and ability to disinfect air, food, surfaces and water, the use of UV-C in ultraviolet germicidal irradiation (UVGI) has become widely accepted over recent years for sterilization and disinfection.

One common application is water purification. In fact, the use of UV-C light to disinfect drinking water can be traced as far back as the start of the twentieth century to a short-lived prototype plant built in France. More successful UV-C-based water treatment facilities started to appear from the mid-1950s and many countries now regularly use UV methods to disinfect water.

UV-C light is commonly used for environmental monitoring using UV spectral absorbance technology
(Water quality monitoring & gas sensing)

Beyond water purification, UV-C light is deployed in air filtration systems and is increasingly used to sanitize medical facilities, workplaces and public spaces.

Because UV-C is readily absorbed by biological materials it is also useful in biological analysis. As well as this, the strong UV-C absorption characteristics of certain gas and liquid molecules mean that UV-C is also beneficial in applications such as gas sensing and detection, liquid chromatography and chemical analysis DNA.

Beyond its use in professional, industrial and scientific systems, recent years have seen a significant rise in mainstream, more consumer-focused deep UV applications such as germicidal lamps and UV-C wands, desk lamps and disinfection boxes.

UV-C Light Sources

Traditionally mercury lamps were the most common sources of UV-C light. These operate by passing an electric arc through mercury vapor to emit deep UV radiation. Low-pressure mercury (LP Hg) lamps typically operate at a wavelength of around 254nm, while high-pressure mercury (HP Hg) lamps emit a broader spectrum.

Mercury lamps suffer from a number of disadvantages in that they are relatively inefficient, require a ‘warm-up’ time, are quite fragile and, because of size and potential contaminant concerns, cannot be readily deployed in all sterilization and sensing applications.

Furthermore, environmental concerns around the use of mercury mean they are subject to ever-stricter regulations and growing calls for their eventual phase-out.

As a result, there is an increasing move to solid-state LED (light-emitting diode) technology as a source of UV-C light for a variety of applications. These include sterilization and disinfection, water quality monitoring of COD (chemical oxygen demand), SS (suspended solid) and nitrate (NO₃), gas sensing for ozone (O₃), emitting sources in medical analyzers and liquid and biological analysis of DNA.

The Rise of the UV-C LED

An LED is a semiconductor device that emits light when an electric current is applied to it. The material properties and design of the LED determine the energy of the emitted photons and, equivalently, the wavelength of the emitted radiation. A UV-C LED is an LED that is specifically designed to emit light in the deep UV spectrum.

While the first commercial LEDs emerged in the 1960s as a source of infrared (IR) light, it wasn’t until the development of LEDs based on gallium nitride (GaN) and subsequently aluminium gallium nitride (AlGaN) semiconductor technology that these devices became practical sources of ultraviolet light.

The use of UV-C LEDs is growing rapidly

Since then, there has been rapid uptake of the technology, not least because using LEDs as a source of UV-C light has numerous advantages over mercury lamp alternatives.

Among these are the fact that UV-C LEDs are less fragile, have a compact size that is ideally suited to small form factor designs, provide much quicker (almost instantaneous) turn-on and turn-off times, and operate at lower voltages. They are also more environmentally friendly than traditional UV mercury lamps.

These considerations, plus an increased global focus on hygiene management and the fight against superbugs thanks to the Covid-19 pandemic, have seen predictions for significant growth of the UV-C LED market. A recent report by market research company Yole Développement, for example, estimated that UV-C LEDs would see a compound annual growth (CAGR) of 61% between 2019 and 2025, resulting in a global market worth in the region $2.5 billion.

Latest Advances in UV-C LED Technology

The Silanna SN3 series is a prime example of how the latest powerful, deep UV-C LED technologies are enabling a new approach to safely and comprehensively incorporating sterilization and disinfection into water quality monitoring. The SN3 series can be utilized in COD and SS monitoring, in gas sensing for ozone (O₃), as an emitting source in medical analyzers and for the liquid and biological analysis of DNA across a wide variety of applications and industries.

New 255 nm UV-C LEDs offer high optical power, small form factors and simplified thermal management

Harnessing the power of innovative new materials and processes, SN3 UV-C LEDs deliver reliable, high-performance operation at low power (typically 0.12 W) in an ultra-compact package that measures just 3.45 mm x 3.45 mm x 1.3 mm.

A typical wavelength of 255 nm and a high optical output power make these deep UV LEDs an ideal, more environmentally friendly and more efficient replacement for low-pressure 254 nm mercury lamps. A low thermal resistance of just 7ºC/W simplifies thermal management, which is an important factor for the performance of the UV-C LED application circuit.

By choosing the latest, advanced UV-C LEDs, OEMs can develop next-generation designs that will address everything from reducing healthcare-acquired infections and food contamination to minimizing the transmission of diseases, removing micro pollutants from drinking water and improving the effectiveness of sensing and analysis systems.