COVER STORY UVC LEDs driving the invisible light revolution
In the last two 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.
In this month’s edition, 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.
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 a single 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.
Considerations when specifying UVC LEDs Depending on the specific application, requirements will vary but there are some general parameters that always apply.
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
10 June 2023 Components in Electronics
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 (next). Bolb Inc. UVC LEDs currently have a light extraction efficiency of next 14% with a roadmap to next 75% in the near future, this compares very favourably with other UVC LED technologies available on the market which are typically next <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.
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