Hygiene and UV-C Lighting

Wim Vinckx, Senior R&D Engineer, Sylvania Lighting

In light of the latest pandemic it has never been so important to sanitise and disinfect.  Crowded areas with poor air circulation (such as public transportation, offices, shops and schools), frequently touched surfaces and recreational water facilities make it easy for pathogens to spread and increase our risk.  Alongside the changes we can make personally in our routines, businesses are also striving to make the places we visit as safe as possible, and one of the most effective ways to do this is with UV-C technology. 

For over 110 years UV-C technology has been used in the sanitisation of air, water and surfaces, and Sylvania is one of the pioneers in the design and manufacture of UV-C lamps.  Whilst some micro-organisms are essential for life, such as in the human digestive system, others can lead to potentially life-threatening diseases, such as COVID-19.  Traditional techniques for the control of pathogens, such as heating, filtration, and the use of chemical agents have some effect, but irradiation by UV-C lamps is considered by far the most effective.

UV-C irradiation has many benefits for use in a variety of applications, the key ones being:

  • Extremely fast purification time
  • East to install, use and maintain
  • Cost-efficient
  • Ecological

So how does ultraviolet sanitisation work?  UV-C radiation has short wavelengths which are more energetic than visible light, and have sufficient power to destroy the DNA and RNA in biological organisms.  The optimum wavelength for this effect is 265nm (nanometre), which falls within the UV-C range. Destroying the genetic code of a micro-organism prevents its cells from reproducing and effectively deactivates them. 

The electrical discharge through mercury vapour in UV-C lamps, such as those manufactured by Sylvania Lighting, produces intense radiation at a peak of 253.7nm.  Not only is this value very close to the optimum of 265nm for deactivating micro-organisms, these lamps are also supremely efficient – with up to half of the power input being converted to UV-C radiation.  No other method achieves such high values.  UV-C LEDs tend to radiate at 275-285nm and although this is also close to the peak germicidal wavelength of 265nm, their conversion of electrical energy into UV-C is at best around 5%.  Therefore ten times more electrical energy is required for the same effect.  This will undoubtedly improve in future and indeed LEDs already have advantages today where small or highly focussed UV-C sources are required, but for many applications they still have a long way to go.

So how do we know that UV-C lamps work on COVID-19?  A prominent study was recently undertaken by the National Emerging Infectious Diseases Laboratories at Boston University1.  In this study UV-C radiation was tested against SARS-CoV-2 and the results clearly demonstrated that a dose of 5mJ/cm2 of UV-C during an exposure of 6 seconds resulted in a 99% reduction of that virus.  This was confirmed by other studies, including Bianco et.al. in Italy2.

We know from academic studies that coronaviruses can survive on surfaces for up to 28 days, however infected people are far more infectious than surfaces.  The primary spread of SARS-CoV-2 appears to be via aerosols, i.e. through the air we breathe. Therefore it’s important to understand what the most effective mechanisms for disinfecting air and surfaces with UV-C are when deciding which method to use for a business.

‘Fresh air’ has always been considered beneficial.  Indoors, however, air can be relatively stagnant or have poor circulation, particularly in cold weather when windows are often kept closed.  Under such conditions air can be a means of carrying infectious organisms into the body.  In some industries, bacteria and mould spores in air can also cause considerable damage to products, resulting in additional costs and a threat to the health of consumers.  Therefore disinfection of air is vitally important.

The good news is that air is easy to purify because it is quite transparent to UV-C, allowing it to penetrate and kill floating pathogens.  Direct irradiation methods can be used based on ceiling mounted lamps which are energised when the room is unoccupied.  Upward radiation mounted safely above eye level, or concealed downward radiation to disinfect floors may under some circumstances be used when people are present.  Alternatively, UV-C germicidal lamps may be mounted within air ducts of a ventilation system which has the advantage that higher UV-C doses can be given because the lamps are out of view – but the disadvantage that since the air is generally moving fast, it flies past the lamps quickly and is irradiated for less time.  Portable standalone units which draw air in, disinfect it and then expel clean air into the room are becoming increasingly popular.  The optimum technique depends on many factors, but since the latter two do not allow escape of any radiation they are considered entirely safe, and can be applied beneficially in nearly all cases.

Pathogens can survive on surfaces for anything from a number of hours to a number of days, depending largely on the material the surface is made from and its roughness.  Cleaning physically removes dirt, organic matter and most micro-organisms from surfaces, but does not always destroy them.  Therefore in some locations, such as hospitals, doctors’ surgeries and offices, it may be important to use a secondary method of surface disinfection such as UV-C direct irradiation. This could be via UV-C robots, open UV-C luminaires, cabinets or a hand-held device.  It is important to note that similar to when light from a window creates shadows when there are objects in front of it, the same happens when treating areas with UV-C rays.  Areas such as seats which are under the desk, areas underneath office equipment etc. will not be reached by UV-C radiation and there will be no benefit.  Therefore UV-C surface disinfection should only be seen as supplementary to chemical cleaning and air purification, but by no means a replacement for that.

One other area where UV-C is currently used is in the disinfection of water.  Clean water is needed not just for drinking but for sanitation and recreational purposes.  UV-C technology is often the most effective, cost-efficient and ecologically friendly mechanism for water disinfection.

Recently there have been a few negative articles about the safety of UV-C light and therefore it is important to stress that UV-C disinfection is safe, but only with the correct safety protocols in place.  Yes, in the case of high UV-C irradiance levels, direct exposure is harmful to humans or animals.  However standards and industry guidelines outline the information and safeguards manufacturers must provide to ensure people’s safety and address foreseeable misuse.  Most UV-C disinfection devices produced by reputable companies have many of the following: Instruction manual and training, timer-control and equipment safeguards (such as a motion sensor).  It is therefore important to source UV-C products from companies with a proven expertise in Germicidal technologies, such as Sylvania Lighting, which will have undertaken rigorous testing and included effective safeguard features in their products3.

As we move through 2021 and the global vaccination programme, we are a step closer to the end of the pandemic.  However one aspect is clear, there will be a sustained increase in the use of UV-C disinfection in the world around us. 

For more information: UV-C@sylvania-lighting.com

  1. Rapid and complete inactivation of SARS-CoV-2 by ultraviolet-C radiation, Research Square, September 2020
  2. Global Lighting Association Paper September 2020 ‘Germicidal Irradiation, Sources, Products and Applications
  3. Global Lighting Association Paper May 2020 ‘UV-C Safety Guidelines’
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