From healthcare and horticulture to cleaning and clubbing, the new generation of small, powerful UV LEDs is making waves in the lighting industry. John Bullock explains.
We don’t spend much time thinking about the parts of the electromagnetic spectrum beyond what we can actually see, but useful work is being done in the outer reaches. The infrared (IR) waveband helps keep us warm and IR thermal imagery is used in all kinds of applications. Ultraviolet (UV) light, on the other hand, is far more complex, with potentially enormous benefits – provided it’s handled with care.
UV LEDs are a significant aspect of the LED revolution. Conventional UV lighting has relied on mercury discharge technology (HID and fluorescent lamps), which has come with an inherent encumbrance due to the physical size and fragility of those light sources.
Recent developments in UV LEDs mean that there is far more scope for the use of UV lighting in healthcare, combating pathogens in our environment and reducing our dependence on chemicals. Use of these small, robust UV LEDs is being considered in environments where conventional UV sources were considered impossible.
It’s not just about the physical size of the UV LED source. The word from the industry is that its power output is growing. A 70mW device was recently launched by Rayvio, a company based in Hayward, California. This is claimed to be the most powerful UV LED currently available. And it won’t stop there.
What is UV?
Ultraviolet (UV) light is part of the electromagnetic spectrum that includes visible light.
As the name suggests, UV exists beyond the violet end of the spectrum.
Visible light exists between 390nm (violet) and 700nm (red); the UV spectrum runs from 400nm down to 100nm and is divided into three sub-groups.
UV-A (315 – 400nm) occurs naturally in sunlight and is created artificially by ‘black lights’. It is used in tanning lamps and to create ‘glow’ effects in some fabrics in entertainment venues.
UV-A lamps have long been known as ‘Wood’s lamps’, after the American physicist, Robert Williams Wood, who first developed the UV light in 1903. They are either linear fluorescent tubes or single-ended high-pressure mercury discharge lamps, familiar by the violet glow that emits from the phosphors.
UV-A lamps are also used in more specialist applications. For example, reptiles have a fourth cone receptor in the eye that sees UV light between 320 – 400nm), and benefit from exposure to UV-A light. UV-A has a place in indoor horticulture, where research has demonstrated that the active compounds in cannabis plants benefit from exposure to UV-A wavelengths. (Further research suggests that the grass grows even stronger under UV-B.)
UV-A LEDs are also making inroads into industrial processes, with high-power LEDs being used in materials curing. UV-A was until recently used in dentistry to set small fillings made from UV-sensitive resin, though new developments in resins means UV light is no longer used.
UV-B (280 – 315nm) also occurs naturally, though much of the solar UV-B radiation is absorbed by the ozone layer that protects us. The UV-B spectrum is known as the ‘biological spectrum’ and it is used to treat skin conditions as well as industrial processes. UV-B lamps are always found in dermatological clinics, and small, domestic units are also available for skin treatment at home. As well as photo-therapeutic uses, UV-B light is also found in industrial applications, such as accelerating the natural hardening or ‘curing’ of glues and resins.
UV-B lamps are available in recognisable forms: fluorescent tubes, double-ended metal halide, CFL and high-pressure mercury reflector envelopes. They are always used in special enclosures to prevent accidental exposure. LED versions have been available in the UV-B range for some time.
Even though much of it gets filtered by the atmosphere, the sun is still a free source of UV-B light for disinfection. Hanging washing on a line in the back garden on a sunny day not only dries laundry, but the sun’s UV-B content helps to deactivate some of the bacteria present in the fabrics. Historically, wool-weaving areas were surrounded by ‘tenter-fields’ full of frames (tenters) for hanging and drying newly made cloth.
UV-C (100 – 280nm) coming from the sun is completely absorbed by the atmosphere, so we create this light artificially. UV-C photons are capable of penetrating organic cells and damaging DNA, making the organisms incapable of reproduction. This is dangerous.
The process kills pathogens such as bacteria, viruses, yeasts and fungi, but does not discriminate between harmful and healthy cells.
Up to now use of UV-C has been confined to sealed systems or rooms where equipment can only be operated once the space is unoccupied. This is about to change. UV-C LEDs offer the potential for powerful but physically small sources, including portable and handheld devices such as the Ellie portable baby bottle steriliser and multi-purpose sanitisation device from Rayvio.
UV-C LEDs are being used to address three major health problems around the world: water purification, air disinfection and surface disinfection.
Water can be purified by passing it through a ‘light bath’ of UV-C light. As the water flows through the light the waterborne bacteria, viruses and pathogens are destroyed in seconds. Laboratory testing with some equipment is demonstrating a 99.9999 per cent efficacy.
Miniaturisation makes it possible to have handheld devices, such as a flask that contains a battery-powered UV-C LED.
Rayvio has reported 99.2 per cent disinfection of E-Coli within 90 seconds when using a single high-power UV-C LED module.
Camelbak offers a UV purifier that claims to turn nearly any tap or clear water source into potable drinking water in 60 seconds.
As so many of us spend a large part of our lives inside buildings with little access to clean air, maintaining good air quality is a vital part of a building’s ‘health’. Cleaning air requires drawing it through a UV-C field, usually within a housing, though not always. As the air passes through the field, the pathogens are destroyed. These systems are often combined with an air filtration system that removes larger organisms (bigger than 0.3 microns).
UV-C LEDs can be used in various ways to purify the air within a room. Air can be drawn through ducts and part of an air-handling system; freestanding air sanitisers can be used in occupied rooms; or ceiling or wall-mounted units can be used to clean unoccupied rooms by radiating UV light freely through the space.
All surfaces can carry bacteria, from the walls that surround us to the phones we carry in our bags and pockets. In some sectors, such as healthcare, science and food processing, it is vitally important that pathogens are controlled and their spread minimised.
Because of their size, UV LEDs are versatile in their application. Trays of instruments can be sterilised by passing them through a UV field, and it is now possible to have handheld UV-C devices that can be used to disinfect equipment while operating in the field.
In the same way as air can be cleaned using room-scale UV projectors, the same equipment can be used to scour walls free of pathogenic materials. And this is where it starts to get really interesting.
Where next for UV?
Eyebrows were raised a little while ago when it was reported that MAG Aerospace Industries was proposing to install a UV LED system into plane cabins. This UV lighting would be triggered automatically once the cabin was unoccupied, demonstrating a perfect example of how our environment can be made healthier with none of the downtime associated with conventional cleaning procedures. Boeing has also revealed plans to incorporate a UV LED cleansing system in plane toilets.
Once we accept the idea that enclosed spaces can be disinfected effectively via UV-C fixtures, the possibilities become obvious. Wherever people are required to spend time in enclosed, shared spaces – train carriages, taxi cabs, hire vehicles, clinic waiting areas – there is potential for incorporating this kind of non-chemical cleansing intervention.
All UV light has the potential to do harm, regardless of the wavelength. Overexposure to a UV-A source will result in tissue damage, though it may take some hours for that to happen. Exposure to a UV-C source can cause lasting tissue damage in a matter of seconds. There are established standards for exposure times and intensities of all UV bands, measured in mJ/cm2. There are Health and Safety obligations around exposure to UV and training courses are available that cover compliance requirements and risk management, dealing with such matters as personal UV exposure limits and hazard awareness.
This explains the public health warnings about protecting skin from too much sunlight. UV light can also seriously damage eyes. It is the impact on DNA that causes the serious damage. UV-B and UV-C photons attack DNA directly, potentially resulting in cancers. And while UV-A had been thought to be less harmful, recent research indicates that UV-A can contribute to skin cancer via the creation of free radicals which, in turn, can damage DNA.
UV-A can cause photokeratitis and conjunctivitis (painful eye conditions) and skin redness (erythema). Effects can be temporary but the impact worsens as the exposure lengthens or as the radiation reaches into the UV-B bandwidths – typical of the intense sunlight experienced in some parts of the world.
UV-B exposure is most likely to come from commercial and industrial processes, though such spaces usually have highly controlled conditions. UV-B health hazards include permanent damage to the eyes (corneal damage, cataracts and macular degeneration, for example) and to the skin (melanomas).
Because UV-C radiation has been used in controlled conditions, there is little actual evidence of UV-C damage. It is worth noting, however, that the European Commission’s Scientific Committee on Health, Environment and Emerging Risks (SHEER) report in February 2017 stated that due to its ‘mode of action and induced DNA damage similar to UV-B, UV-C is considered to be carcinogenic to humans’. As with UV-B, exposure to UV-C is always under tightly controlled conditions.
Now that we’re producing UV-C LEDs that are more powerful than anything yet seen, able to be incorporated into handheld devices, it’s important to reiterate one simple fact: human beings are generally made up of the same stuff as the things that UV-C lighting is trying to kill. Handheld devices can be extremely useful, provided you don’t point them at yourself or other innocent creatures. As use of UV-C light proliferates in the form of these small LED modules, it will be vitally important to ensure that all equipment comes from responsible sources, is built to appropriate standards and equipped with the necessary safety devices to guard against accidental exposure.
- We must insist that all UV-C devices are fitted with visible light indicators that tell us when the equipment is working. Sensors need to be incorporated, such as the gyroscopic sensors in smartphones, that can switch a device off if it is being held inappropriately.
- Radiation can be a problem even where UV light isn’t present. Handheld devices, such as those used in dentistry, include a physical light filter to stop reflected light reaching the operator’s eyes when the device is in use.
- As UV-C radiation is used in enclosed spaces to provide surface and air disinfection, installations must be fitted with presence detection to protect accidental trespass into an area being treated.
There is no reason why UV-C radiation for disinfection cannot be achieved safely. It will all come down to the quality of the product and the environmental design.
Safer than soap?
There is a trade-off between benefit and risk. The use of UV lighting means that we can use less antibacterial chemicals. The two most common antibacterial agents in soaps are Triclosan and Triclocarbon. Triclosan has been identified as a promoter of super-bugs –bacteria resistant to antibiotics. There is also evidence of Triclosan being found in the umbilical cord blood of newborns and in mothers’ breast milk. And as if that’s not enough, about 75 per cent of Triclosan and Triclocarbon survives flushing through the sewerage system, ending up in waterways and on cultivated fields. And to cap it all, antibacterial soaps don’t actually work. There is no evidence that these products prevent disease in the home. So there may be very good reasons for a shift towards antibacterial treatment using UV LED light.