10
UV BASICS
Ultraviolet light belongs to the electromagnetic spectrum with a wavelength between 200 and 400 nm (nanome-
ters), which is shorter than visible light, but longer than X-rays. All UV rays and bands are invisible to the human
eye.
The UV spectrum can be divided into the following bands:
UV-A (Long Waves; 400-315 nm): Used for Black Lights, Skin Tan, Ink/Resin Hardening.
UV-B (medium waves; 315 – 280 nm): used to treat psoriasis, may cause sunburn, skin cancer.
UV-C (short waves; 280 – 200nm): more effective for germicidal disinfection.
UV-V (UV under vacuum, less than 200 nm): may produce ozone in the air.
All of the above wavelengths of UV light are emitted from the sun, but only the longest wavelengths, UV-A
and UV-B reach Earth. UV-C rays, which are the shortest wavelength but the highest energy, are blocked by the
ozone layer.
INACTIVE MICRO-ORGANISMS
Because UV-C rays are blocked by the ozone layer, micro-organisms have not developed a natural defence
against UV-C energy. When the DNA of a micro-organism absorbs UV-C energy, molecular instability occurs,
resulting in interruption of the DNA sequence. This makes the cell unable to grow or reproduce. Without the
ability to reproduce, the cell cannot infect and dies quickly.
The application of UV-C energy to inactivate micro-organisms is
known as germicidal irradiation or UVGI. It has been used for this
purpose since the early 1900s. Artificial UV-C energy is produced
in germicidal ultraviolet lamps that produce UV radiation by ion-
ising mercury vapour at low pressure. These lamps are similar to
typical fluorescent lamps for domestic use, but do not have the
phosphorescent coating that transmits soft white light. Most com-
mercial UV-C lamps are low-pressure mercury lamps that emit
UV energy at 253.7 nm, which is an ideal wavelength for disrupt-
ing the DNA of micro-organisms.
UV-C lamps and devices are increasingly used worldwide in vari-
ous configurations and applications to disinfect water, air and sur-
faces.
