LED Technology
robotics to control the application of UV-C, which in turn helps reduce a key drawback of light-based sterilisation: the effect of shadowing. The light can only sterilise surfaces that it hits, which can make it difficult to fully sterilise a room with beds and medical equipment present because they will obstruct each other. Robots can analyse shapes and compute trajectories that will maximise area coverage and combat the effects of shadowing. Though early projects such as one trialled for disinfecting buses in Shanghai used manually placed light sources and fixed arrays in a covered bay around the outside of the vehicle, the use of mobile robots makes it easier to ensure surfaces that would normally be shadowed with fixed illumination, such as the backs of seats, can now be covered. In a similar fashion, mobile robots could ensure UV-C is spread evenly within a hospital setting while a treatment bay is empty. Even with basic coverage, UV-C treatment has been shown to be more efficient than manual cleaning with disinfectant. The UV-C irradiation can be done in less than ten minutes compared to 40 minutes for chemical treatment.
Cost and availability are key factors LED technology, in turn, addresses the issue of availability for cost-effective light sources. LEDs have long been able to produce UV light. The LED is an important component of many lighting products where a white phosphor is used to convert UV generated by an LED array, based on gallium nitride materials, into usable visible light. However, the shorter wavelengths in the UV-C band call for novel forms of material that incorporate gallium nitride.
Today’s UV-C LEDs use aluminium gallium nitride (AlGaN) rather than the indium gallium nitride (InGaN) that is used in blue and green LEDs. There is sufficient commonality between them to use similar epitaxy processes, which means either gallium nitride, silicon or silicon carbide wafers can be employed. The key difference is the need for the wafers to be able to handle higher temperatures during processing. Temperatures of up to 1400°C are needed to deposit high-quality AlGaN crystals through epitaxy.
High intensity UV-C products for decontamination
Manufacturers have solved the production issues and are now coming to the market with high-effi ciency UV-C sources based on LED technology. Osram Opto Semiconductors launched a pair of UV-C LEDs with a peak
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wavelength of 275nm. The SU
CULBN1.VC is optimised for low-power usage, suitable for portable applications or household equipment, with an output radiant fl ux of 4.7mW and 120° angle of half intensity. With the same angle of half intensity and an emission output of up to 42mW, the SU
CULDN1.VC suits applications that need high levels of UV-C coverage over a large area, such as vehicle cleaning or large- scale air and water treatment. A key factor in the design of the two Osram products is the use of a single package footprint. By using a single package size, the products support the design of equipment ranges that allow different target markets to be covered with a single mechanical enclosure. The use of a ceramic package design offers long operational lifetimes and thermal resistance.
With a 60° angle of half intensity and an output flux of 3.5mW, the VLMU35CL2.-275-120 produced by Vishay Semiconductors suits designs that call for targeted applications of UV-C. The CB2 and CT2 members of the product line increases the output flux to up to 10mW and 19mW respectively for systems that need to produce higher-intensity radiation in the 270nm to 285nm wavelength range. Products in the Vishay range are suited to industrial applications that need an extended temperature range, with the ability to operate from -40°C up to +80°C.
For systems that need specific combinations of output flux, wavelength and illumination angle, Intelligent LED Solutions (ILS) has developed a wide selection of products based on the LED technology of TSLC. The N3535 and N5050 families allow selection of wavelengths in the 260-270nm and 270-290nm UV-C ranges in addition to the 300-320nm range. This enables fine tuning of the output to target different pathogens.
Optics and measurement are critical in UV-C design
Conventional glass is not transparent but both quartz and silicone will allow UV-C to pass through. The conventional silicone employed in other LEDs can degrade under intense UV-C irradiation, but suppliers have developed new formulations that allow the silicone to survive. A common packaging design is to couple a quartz window with a silicone focusing lens. To aid the design of area irradiation systems, ILS offers the LEDiL VIOLET Optic. This is a silicone 12-lens array to allow the easy copackaging of multiple UV-C light sources and is available in 3 beam angles of 14, 20 and 60 degrees to allow for further design fl exibility.
With a wavelength that is outside the visible range and is as hazardous to health as it is to viruses, the ability to monitor UV-C emissions safely during
design is a vital requirement. The SDL470 UVA/UVC Light Meter and Datalogger manufactured by Extech Instruments provides the means to record over long periods the performance of UV light sources. The datalogger has probes for UV-A as well as UV-C at 254nm, which is typically generated at lower levels by the sterilisation products that normally peak around 270nm. Sampling rate can be adjusted from one to 3600 seconds to allow a tradeoff between long-term recording capacity and temporal resolution. UV-C disinfection, with the help of LED technology, is driving the creation of many novel applications for a wide range of markets, however design-in support will be critical. Experienced technical distributors such as Farnell can provide professional advice and support to help engineers identify products that are the best fit for their applications. Design engineers should consider market-leading suppliers that are pioneering the development of UV-C technology to source solutions for their next project. The successful combination of sensor-driven AI in robotics and automation with market-leading innovations in LED technology has the potential to make the healthcare benefits of UV-C more accessible to society.
https://uk.farnell.com Components in Electronics November 2021 33
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