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How LED technology is creating new solutions for infection control, more efficient streetlighting, and healthier indoor spaces
By François Mirand
EMEA Technical Director, Future Lighting Solutions
The LED lighting industry has been an exciting field in which to work over the past 20 years because its technology develops at a rapid pace. This creates not only the opportunity to improve the design of existing types of fixtures, but also to create entirely new applications for lighting. Who imagined 20 years ago that the shape and illumination pattern of something as simple as a car’s indicator light could become an important part of the brand signature of a premium marque such as Audi? Or that the street scene in cities all around the world would be newly filled with well rendered color at night thanks to LED streetlights?
The innovation continues apace. So which LED technologies are expected to enjoy fast growth as we move into the middle years of the decade?
New appreciation of hygiene and disinfection
The hygiene lessons of the Covid-19 pandemic are not going to be forgotten in a hurry. The increased attention paid to disinfection and decontamination has helped to stifle the transmission of coronavirus, of course, but has also contributed to lower rates of infection with influenza, the common cold and other diseases. And there is now a broad public understanding that regular disinfection will help to stop the spread of the new strains of Covid which emerge from time to time.
New optoelectronics products have their part to play in the battle against transmission of infection: interest in the germicidal properties of ultraviolet (UV) light is increasing rapidly. In response, LED manufacturers are developing products which can provide an efficient and powerful light output in the UVC portion of the spectrum, which covers wavelengths between 100 nm and 280 nm.
Established suppliers such as Nichia and Seoul Viosys are vying with newcomers such as Luminus Devices to increase efficiency, lower the cost-per-photon, and scale up production capacity. Crucially, manufacturers are now producing UVC LED products with output power above 100 mW. Luminus for example has released the XFM-5050, a four-chip package producing a maximum optical output of 480 mW.
At the same time, the cost of UVC LED light has fallen below 20 cents per mW and is edging closer to 10 cents per mW, which is seen as a tipping point by many equipment manufacturers. Efficiency in mass production parts has jumped from around 1.5% to more than 3%. Experts foresee rapid progress towards 10% efficiency.
In parallel, manufacturers of optics for LEDs have qualified new materials and released dedicated products which are both efficient, and resist degradation by UVC light. The increased power and efficiency of UVC LED light sources is leading product manufacturers to explore applications for air and water purification as, to date, UVC LEDs have been used primarily for surface disinfection. UVC LEDs are particularly suitable for disinfection of indoor air when placed at ceiling height, which is known as upper-room air disinfection: the very small light-emitting surface of a UVC LED enables tight beam control. For example, a Seoul Viosys linear UVC light module can be paired with the LEDiL VIOLET RS optic to make an ideal off-the-shelf light engine, as shown in Figure 1a.
Fig. 1a: The LEDiL VIOLET-12X1-RS combined with a linear UVC LED module such as the Seoul Viosys XMD-FBC-LLCA may be used in upper-room air disinfection applications. (Image credit: LEDiL)
Fig. 1b: The LEDiL VIOLET-RS optic for UVC LED linear modules. (Image credit: LEDiL)
Following the IES volumetric dosing guideline of 12 mW/m3, such a UVC light engine would cover approximately 10m3, or 4m2 in a room with a 2.5m high ceiling, burning around 10 W of electrical power. The LED unit is itself much smaller than a mercury tube. What’s more, the mercury tube requires a large reflector to shape its 360° irradiation to a narrow beam.
Compact and lightweight, the UVC LED unit can be added to existing lighting fixtures, or integrated into future designs, to add the value of indoor air disinfection to the standard visible illumination function, or to operate in stand-alone air disinfection mode.
The adoption of UVC LEDs in municipal water treatment works is also forecast to gather pace after the first installation in 2020. The use of UVC irradiation to eliminate microbial contamination from water supplies is well understood. Using LED technology, manufacturers can realize new, more compact reactor designs which fit in the limited available space in existing plants, greatly reducing or eliminating the cost of building work to create space for disinfection equipment. In addition, as shown in Figure 2, the use of LED technology entails lower maintenance cost and effort than conventional UVC emitters.
Fig. 2: The first UV LED-based water treatment units installed near Carlisle, UK. (Image credit: Typhon Treatment)
Innovation in LED formats for streetlights
While development in the UVC LED field has centered on the fundamental performance of the emitter, in the LEDs used in streetlights, manufacturers are bringing their powers of innovation to packaging, production and reliability.
Until recently, streetlight designs were based on the use of single-chip, high-power LEDs. Now, however, the manufacturers of streetlights are overcoming their objections to the use of newer LED platforms: multi-chip high-power LEDs such as the popular 5050 package; and mid-power LEDs, generally in the standard 3030 format.
This move has been possible because LED manufacturers have improved the reliability of these newer products. In particular, sulfur resistance has been improved, and L90 lifetime projections can now exceed 100,000 hours. Lumileds is a good example of the progress that has been made: its LUXEON 5050 Square LED is a popular choice for streetlights. Its XR-5050 SQR modules, shown in Figure 3, are compliant with the Zhaga Book 15 footprint and meet the most stringent tender requirements.
Fig. 3: The Lumileds XR-5050 SQR module. (Image credit: Lumileds)
The benefits of using these newer LED types include:
Innovation is also reshaping the market’s approach to control and networking of arrays of streetlights. Europe has been at the forefront of this move, leading the standardization of control interfaces for streetlights. Zhaga and DiiA have joined forces with the IES to back the D4i standard; and ANSI C136.41 receptacle-based hybrid architectures are to be added to the Zhaga Book 18 Edition 3.0.
This is enabling streetlight manufacturers to develop future-proof designs under the Zhaga-D4i standard umbrella ready to support both local and remote control, as well as 5G deployment further in the future. The D4i roll-out is also finding support among driver manufacturers: Inventronics with its EUM series, for example, was the first to qualify IP67-rated drivers to the D4i standard.
Diverse approaches to ‘natural’ lighting
Moving indoors, the lumen-per-Watt race attracts far less attention than before, and LED manufacturers now compete to introduce innovations which improve the quality of light. Color rendering is one important parameter of quality: mainstream LEDs today generally offer 80 CRI and 90 CRI variations. In the premium LED market, 95 CRI has become more common and several LED manufacturers now specify, in addition, an R9 value: Nichia has released chip-on-board (CoB) LEDs which offer minimum Ra 95 and R9 80 values.
Uniformity is another challenge for manufacturers which seek to meet lighting designers’ strictest demands for quality of light. Here, Lumileds with its LUXEON Deep Dimming products and Nichia with its 757-MT are providing new solutions for luminaires implementing deep DC dimming or tunable white lighting.
Meanwhile, the jury is still out on the question of the best way to stimulate public appreciation of the concept of natural or ‘human-centric’ lighting (HCL). Scientific consensus about spectral effects on human health is similarly hard to find. Nevertheless, the choice of LED sources for HCL grows apace. It includes both full-spectrum LED sources such as the Seoul Semiconductor SunLike range, Nichia’s Optisolis™ LEDs or the Bridgelux Thrive™ family; and color-enhanced products such as Nichia’s Vitasolis™ and Dynasolis™ families or the Luminus Salud range.
Real-world deployments remain scarce, but a 2020 study by the Fraunhofer Institute for Building Physics on the perception of full-spectrum LEDs, which found support for the claims of advantages in HCL over conventional LED lighting, could spark renewed interest.
One expression of HCL is circadian lighting, in which the color temperature is adjusted throughout the day to match the natural spectral variation in sunlight, and to mimic the spectral characteristics of natural firelight at night. Bridgelux provides a way to ease the implementation of the tunable white systems required for circadian lighting with its Vesta® Flex drivers and Vesta Thrive LED modules. This turnkey solution includes full-spectrum tunable white LED light sources, dual-channel drivers and control interfaces which support both standard 0 to 10 V, DALI and Qualified Bluetooth® mesh systems, as well as proprietary control protocols.
Qualified Bluetooth mesh, also known as SIG mesh, has become the wireless control protocol of choice for indoor lighting, and has been adopted by important players in the industry. The standard has delivered on the promise of interoperability: compliant devices from different manufacturers can be commissioned using tools such as the Silvair platform to form a functional lighting control network.
The release of the Mesh Device Properties v2 specification in September 2020 has unlocked more IoT capabilities beyond simple lighting control, enabling detailed diagnostics and reporting of maintenance events. Companies such as Silvair are already integrating these new capabilities into their firmware and commissioning applications. Silvair’s implementation of stand-alone scheduling, requiring no gateway, is an important move which will make it easier to design and deploy circadian lighting systems.
Technology trends to follow
Future Lighting Solutions can see today the evidence of rising demand for the technology developments described above. But looking further ahead, innovations already in the pipeline are set to excite further interest.
In streetlighting, the deployment of 5G mobile networks will have a profound impact. The massive machine-type communication (mMTC) feature in 5G will enable new central monitoring capabilities encompassing municipal lighting. There is great promise in efforts to make streetlights the IoT hub of smart cities. Streetlight poles are also an ideal host for the 5G microcells required to provide dense network coverage in urban areas.
And the collaboration between the Bluetooth Special interest Group and the DiiA will undoubtedly fuel the adoption of both D4i and Bluetooth mesh in indoor lighting following the release of Zhaga Book 20.
The rate of innovation in LED technology, then, gives great cause for optimism as the world emerges from its Covid-induced slump, and the prospects appear particularly strong in UV LEDs, streetlighting and HCL.
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