How effective are UVC LEDs?

Answered by the technical team at RayVio corporation.

Ultraviolet (UV) light has been used for many years in industry and in health and hygiene regimes. A new generation of LEDs now looks set to challenge conventional UV fluorescent sources. But how well do they actually perform?

 

 

What is the wavelength range of UVC LEDs?

UVC LEDs are typically defined as having a wavelength on the electromagnetic spectrum of 200nm to 280nm.

What is the ‘germicidal range’ of ultraviolet light?

According to the International Ultraviolet Association:  “The portion of the UV spectrum (the ‘germicidal’ region) that is important for the disinfection of water and air is the range that is absorbed by DNA (RNA in some viruses). This germicidal range is approximately 200-300nm.”  

The germicidal range is known to extend beyond 280nm and is now generally thought to extend to 300nm, although this too may change with more research. Scientists have proved that wavelengths between 280nm and 300nm are germicidal and can be used for disinfection and sterilisation.

 

What is the optimum wavelength for disinfection?

There is a misconception that 254nm is the optimum wavelength for disinfection because the peak wavelength of a low-pressure mercury lamp (simply determined by the physics of the lamp) is 253.7nm. A wavelength of 265nm is generally accepted as the optimum as it’s the peak of the DNA absorption curve. However, disinfection and sterilisation occur over a range of wavelengths.

UV mercury lamps have been considered the best choice for disinfection and sterilisation. Why is that?

Historically, mercury lamps have been the only option for disinfection and sterilisation. With UV LED technology advances, there are new options that are smaller, more robust, toxin-free, long lived, energy efficient and allow for infinite on/off switching. This allows solutions to be smaller, battery powered, portable and with instant full light output.

Spectral emittance of low-pressure mercury UV lamp (solid line) and medium-pressure mercury UV lamp (dashed line)

How do the wavelengths of UVC LEDs and mercury lamps compare?

Low pressure mercury lamps emit an almost monochromatic light with a wavelength of 253.7nm. Low-pressure mercury lamps (fluorescent tubes) and high-pressure mercury lamps are also used for disinfection and sterilisation. These lamps have a much broader spectral distribution that includes germicidal wavelengths. UVC LEDs can be manufactured to target very specific and narrow wavelengths. This allows solutions to be tailored to the particular application need.

 

Are the DNA peak absorption wavelengths different depending on the germ?

Yes, peak absorption rates do vary from germ to germ, though most are around 265nm.

 

Can a single wavelength be used to disinfect for all germs?

Yes, a single wavelength can be used. However, germs have different optimum absorption wavelengths.

 

How is germicidal effectiveness determined?

Power intensity, wavelength and exposure duration are typically used to determine germicidal effectiveness. For instance, in water there may be multiple germs with different optimal absorption wavelengths. For any given wavelength of germicidal UV light, the power and duration of exposure would need to be calculated in order to achieve the desired level of disinfection.

 

Are there different levels of disinfection or effectiveness?

Yes, there are actually six levels of disinfection based on the reduction factor. If we start with a population of one million bacteria, one would measure disinfection effectiveness as follows:

  • Reduce the colony to 100,000 bacteria – 90 per cent reduction
  • Reduce the colony to 10,000 bacteria – 99 per cent reduction
  • Reduce the colony to 1,000 bacteria – 99.9 per cent reduction
  • Reduce the colony to 100 bacteria – 99.99 per cent reduction
  • Reduce the colony to 10 bacteria – 99.999 per cent reduction
  • Reduce the colony to one bacterium – 99.9999 per cent reduction.

 

For further information see the US Environmental Protection Agency’s ‘Ultraviolet disinfection guidance manual for the final long term 2 enhanced surface water treatment rule’.

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John Bullock: askjohn@luxreview.com

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