It has been known more than 100 years ago that Ultraviolet (UV) light has a germicidal effect. The natural source of UV light is the sun. It emits about 10% of its energy in the UV region. However since it is mostly blocked by the earth’s atmosphere it has no germicidal effect in our immediate environment, like our home’s indoor air quality or our water systems.
Ultraviolet is a spectrum of light just beyond the visible range. UV light is divided into four ranges of wavelengths:
- (1) Vacuum UV from 100 to 200 nanometers,
- (2) UV-C from 200 to 280 nanometers,
- (3) UV-B from 280 to 315 nanometers, and
- (4) UV-A from 315 to 400 nanometers.
The UV-C spectrum (200 to 280 nanometers) is the most lethal wavelength for microorganisms, because it disrupts the chemical bonds between the atoms which, in biological terms, results in a “dead” microorganism. This range of wavelengths is also known as the Germicidal Spectrum. The germicidal spectrum is used to destroy bacteria, mold, viruses and other biological contaminants in the air, in liquids, or on surfaces.
UV light can be artificially generated by UV Lamps. UV Lamps are commonly referred to as Germicidal Lamps. Germicidal UV lamp purification has a long history and it is widely used for air purification, water treatment and surface disinfection purposes. It is a cost effective, environmentally friendly solution. Its effectiveness is directly related to intensity and exposure time. Ultraviolet germicidal lamps are low pressure mercury vapor lamps that are producing ultraviolet light by electrical discharge. The produced electromagnetic energy (UV light) has a lethal effect to microorganisms. Ultraviolet light is used in industrial and residential applications to purify water, air and surfaces.
The effectiveness of UV Lamp is limited by ambient temperature because of the inherent characteristics of the mercury. The most optimum ambient temperature range for standard low pressure UV lamp is between 65-85 °F or 18-29 °C. This means that if the ambient temperature goes below or above this range the effectiveness of the UV light intensity decreases. Depending on the application the UV lamps are normally protected inside of a glass tube to avoid large temperature changes.
The amalgam technology in ultraviolet lamps enables optimum mercury vapor pressure at wider temperature range between 35-120 °F or 2-49 °C. In the Amalgam Ultraviolet Lamps the mercury is alloyed with Indium forming an amalgam of the two metals. The amalgam is placed along the inside axis of the quartz tube. This provides the optimum mercury vapor pressure at higher lamp temperatures. The benefit is that the UV output intensity of the amalgam lamp is not affected when the ambient water temperature fluctuates over a large temperature range. Water temperature will fluctuate in any typical Water Treatment Plant mainly due to weather conditions and flow rates. Maintaining a constant output over a large ambient temperature range is critical to the performance of a UV system because if the intensity of the ultraviolet lamp falls, the kill rates of microorganisms will decrease dramatically.