What is UVC?
Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, that is, in the range 10nm to 400nm.
It is so-named, because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the colour violet. These frequencies are invisible to humans, but visible to a number of insects and birds.
The electromagnetic spectrum of ultraviolet light can be subdivided in a number of ways. The ISO standard on determining solar irradiances (ISO-21348) describes the nine different ranges and Ultraviolet C range (UVC) is defined as wavelengths from 100nm to 280nm. UVC radiation is also often called germicidal radiation because of its ability to destroy micro-organisms such as pathogens, viruses and moulds.
At certain wavelengths (typically from 245nm to 275nm) UVC is mutagenic to bacteria, viruses and other micro-organisms. It will break the molecular bonds within micro-organismal DNA, producing thymine dimers in their DNA thereby destroying them, rendering them harmless or prohibiting growth and reproduction.
What is a UV lamp?
The UVC radiation is generated by UV lamps. UV lamps contain a small amount of mercury or mercury alloy, either in a free state within the lamp tube, or embedded within the lamp tube’s surface. The UV lamps can be either conventional (with electrodes) or electrodeless. When a voltage is applied to the electrodes of conventional lamp, electrons flow between them and vaporise the mercury. Plasma is created within a lamp and emits UV light. For the electrodeless lamps, the energy to ignite plasma is delivered to the lamp by electromagnetic waves (microwaves). The exact wavelengths emitted, depend on the vacuum pressure within the lamp tube itself when operating.
Low Pressure (LP) UV lamps work at relatively “low” pressures (between 1-10 Pa) and emit germicidal (i.e. UVC) light at a single UVC wavelength of approximately 254nm. Medium Pressure (MP) lamps work at what is termed “medium” pressure and emit a broader spectrum of UV light with higher intensities between around 254 - 265nm.
For air disinfection applications, low pressure UV lamps are preferred, due to their higher energy efficiency (usually around 30%).