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

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 sterilization.

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 sterilization occur over a range of wavelengths.

Historically, mercury lamps have been the only option for disinfection and sterilization. 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)

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 sterilization. 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.

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

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

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.

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.