UVC LEDs driving the invisible light revolution

UVC LEDs driving the invisible light revolution

In the last 2 decades the lighting world has seen a revolution as lighting systems have transitioned from using incandescent and fluorescent light sources to solid state LEDs, this has led to increased reliability, lower power consumption and improved quality of light. A similar revolution is now beginning in the UVC market, LED replacements are now available offering benefits vs. traditional mercury based lamps. David Pearson, Technical Director at Anglia, looks at some of the main considerations when specifying UVC LEDs along with an overview of some typical use cases and key technology advantages of Bolb Inc. LEDs.

 

Why UVC LEDs?

The pandemic highlighted an important need for convenient, safe, effective and environmentally friendly disinfection that does not involve harsh poisonous chemicals. UVC has a vital role to play. Whilst UVC LEDs still lag behind mercury based lamps in terms of output, the gap is closing. UVC LEDs offer several important advantages over mercury lamps, which opens up new applications and use cases where traditional mercury based lamps would not be suitable.

One of the most significant is that it is possible to provide optimal beam control with LEDs using optics and reflectors to improve how radiated energy is focused. Furthermore, UVC LEDs do not contain mercury or generate ozone like traditional lamps, they start instantly and do not require a warm-up phase, making them suitable for applications with high switching cycles. And finally, UVC LEDs are not made of glass making them more resistant to impact and vibrations and eliminating the risk of mercury leakage that can occur when conventional lamps break.

Considerations when specifying UVC LEDs

Depending on the specific application, requirements will vary but there are some general parameters that always apply.

Safety first

UVC light can be harmful to living organisms and can damage DNA and RNA. Exposure lasting just a few hours can irritate the skin and eyes, with long-term exposure increasing the risk of cancer. It is therefore essential that users are not exposed to UVC light for extended periods of time. UVC light cannot be seen, or in some cases only as a dim purple light, this makes it even more important to ensure that UVC based systems are safe for the people who use them.

No matter what wavelength of UV radiation is used, the safety of the system is paramount, below are some essential safety recommendations:

• ·        Install LEDs in an enclosure to avoid leakage of light.
• ·        If LEDs are not placed in an enclosure, users of UV light technology must wear appropriate personal protection equipment.
• ·        Use smart solutions such as sensors, control timers, and connectivity to limit exposure.
• ·        Place appropriate warnings on the product packaging and device.
• ·        Provide education and training to all users.

Wavelength

The three main types of UV light are UVA (320–400 nm), UVB (280–320 nm), and UVC (200–280 nm). The UVC region is the most important for disinfection as it offers the highest ultraviolet germicidal effect.

Conventional mercury lamps are limited to single a peak wavelength of 254 nm. Whereas UVC LEDs can be produced in specific wavelengths, for example 275 nm, or 265 nm. Germicidal effectiveness in individual cases does vary depending on the target medium, surface, and microorganisms but it is generally accepted that the 260–270 nm wavelength range offers the highest rate of disinfection.

Efficiency

Wall Plug Efficiency (WPE) of the light source, also known as Power Conversion Efficiency (PCE). The WPE or PCE is the ratio between the optical and electrical power of the emitter. Currently, UVC LEDs typically deliver 260–280 nm with efficiencies ranging from ∼ 1% to ∼ 10%. So, for example a UVC LED producing 100mW of optical power could consume between 10W and 1W of electrical power depending on its WPE. This parameter is especially important with large scale deployments of UVC LEDs such as those used in water treatment reactors.

Optical Output

Optical output is another essential factor, UVC LEDs have output specified in milliwatts or watts at their typical driving current and forward voltage. To increase the optical output of an LED, you can simply increase the driving current up to the maximum current specified. LEDs can also be easily collimated using optics or reflectors to precisely focus the UVC light. However, note that not every material is compatible with UVC light. For example, standard glass can block UVC rays and standard plastic optics degrade when they are exposed to UVC light. That’s why optics made of quartz glass or silicone material are recommended.

As one of the leading drivers of the UVC LED revolution, Bolb’s technology allows for greater optical output by employing a chip construction with a unique transparent layer and an efficient hole injector layer. This patented technology allows efficient extraction of light from the device and increases the amount of power emitted externally (ηext). Bolb Inc. UVC LEDs currently have a light extraction efficiency of ηext 14% with a roadmap to ηext 75% in the near future, this compares very favourably with other UVC LED technologies available on the market which are typically ηext <6%.

Lifetime

The lifetime of UVC LEDs is heavily dependent on the usage conditions. The driving current of an LED is inversely proportional to the lifetime, e.g., higher current reduces lifetime. A simple formula can be used, lifetime is extended or shortened by the inverse of the current ratio to the power of 1.5.

As with any LED, operating temperature also influences lifetime and optical output. Exceeding the recommended ambient, solder, or junction temperature will have a negative impact on the lifetime. UVC LEDs must be properly cooled to avoid accelerated optical power loss and/or shortened lifetime. The use of appropriate cooling solutions, for example metal core PCBs, thermal pastes, heat sinks, or heat pipes and fans, is prerequisite, particularly in applications where significant optical power is required and where the LED density is high.

Dosage

Finally, it is essential to look at the UVC dose that is required. The dose depends on the type of microorganism that you want to target (several studies include UVC radiation tables), and on the type of application. The system developer needs to carefully consider the target medium, is it a surface, an object, or a fluid? the characteristics of the material, the distance to the target and how quickly should disinfection be completed.

Applications

UVC can be effectively used to disinfect Water, Air, Surfaces and Food.

Water - Disinfection can be done at Point of Use (PoU) and at Point of Entry (PoE). UVC disinfection does not alter the taste, temperature, or pH of water. Due to their compact dimensions UVC LEDs can be integrated into PoU disinfection systems for water faucets, fountains, and water bottles where conventional light sources cannot be used. Typical uses include laboratories for ultrapure water, in homes, and in mobile water disinfection systems.

PoE is a much more demanding application, primarily due to the high flow of water and continuous demand cycle. Nevertheless, Bolb Inc. are already working with early adopter companies that have begun installing high-flow water disinfection reactors. These systems can be used in municipal water treatment plants, swimming pools, fish farming, ballast water treatment systems on ships, and in many industrial applications.

Air - UVC light has a significant impact in preventing transmission of airborn viruses. Air disinfection systems can be deployed in classrooms, offices and public transport. Devices already come in many forms, for example mobile units, air troffers, air ducts, and upper air disinfection solutions. With UVC LEDs, new, innovative solutions for clean and healthy air are possible, from retrofitting into existing systems to development of completely new applications. The “single pass kill rate”, in other words the amount or percentage of virus that will be killed in one pass through an Air disinfection device is considered a key parameter. LED systems have been developed that can disinfect an air flow of 10,000 litres per minute and achieve a 99.96% kill rate in a single pass against aerosolized Staphylococcus aureus. This is with just one 25-LED module with 2.5 W of optical power.

Surface – UVC LEDs offer a simple way to disinfect objects and surfaces that need to be kept free of viruses, bacteria, or mold. They can be deployed in hospitals, for medical equipment, in forensics, and where objects are regularly touched, for example door handles, handrails, ATMs, restaurant menus, etc. For surface disinfection systems, designers must take particular care to ensure safety because this is where users face the highest risk of exposure to UVC radiation.

Food - Essentially a combination of water and surface disinfection, food disinfection is worth mentioning separately, as food loss due to bacteria or fungus can be crucial. In addition, food poisoning is a well-known risk, its increasingly common for recalls on salad, vegetables and meat after treatment with contaminated water used in the process. From seeds, to plants, to fruit and vegetables, as well as in livestock breeding, UVC LEDs can be used in many applications. They can also be put to good use in disinfecting farms, greenhouses, vertical farms, food processing factories, and kitchens, as well as in food transport, storage, and retail. Not only do they help to prevent food waste, UVC LEDs can also significantly reduce the use of pesticides, chemicals, and antibiotics in the farming industry.

Design support

Anglia offers support for customer designs with free evaluation kits, demonstration boards and samples of Bolb Inc. products via the EZYsample service which is available to all registered Anglia Live account customers.

Anglia’s engineering team are also on hand to support designers with UVC based designs and can offer advice and support at component and system level. This expertise is available to assist customers with all aspects of their product design, providing hands on support and access to additional comprehensive Bolb Inc. resources which includes technical application notes, case studies, whitepapers and reference designs to help designers select the right product for their application.

Visit www.anglia-live.com to see the full range of Bolb Inc. products available from Anglia.

Article based on original content reproduced with kind permission of Paul Blanc, European Sales Director for Bolb Inc.

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