Ultraviolet lamp (UV light)

Wednesday, 17 January 2007

The use of ultraviolet (UV) light or radiation for its purification, germicidal and bactericidal effect is well known. When administered at the desired frequencies, durations, and intensities, ultraviolet (UV) light is able to kill a wide array of micro-organisms that include bacteria, viruses, spores, algae and protozoa, without having to chemically treat the object to be disinfected. Ultraviolet light is generally viewed as light having wavelengths less than about 400 nanometers (nm), which is about the shortest wavelength of light that the human eye can perceive as violet in color, and greater than about 200 nm. Ultraviolet radiation can be generally divided into three components, each characterized by different wave lengths: ultraviolet A (from 315 to 410 nanometers), ultraviolet B (from 280 to 315 nanometers), and ultraviolet C (from 200 to 280 nanometers). The germicidal effect is caused by ultraviolet C radiation, and specifically, radiation having a wave length of 253.7 nanometers. It deactivates the DNA of bacteria, viruses and other pathogens and thus destroys their ability to multiply and cause disease, effectively resulting in sterilization of the microorganisms. Specifically, ultraviolet C light causes damage to the nucleic acid of microorganisms by forming covalent bonds between certain adjacent bases in the DNA. The formation of these bonds prevents the DNA from being "unzipped" for replication, and the organism is unable to reproduce.

Ultraviolet radiation has long been known to have a number of positive purification, germicidal and bactericidal benefits. UV light is commonly used to control the growth of and kill impurities in septic, water and air systems. For example, UV lamps are used in heating, ventilation, and air conditioning (HVAC) systems for purification or air cleaning purposes. UV lamps are typically installed or mounted in the air ducts of HVAC systems in such a manner that the UV light emitted by the lamp floods the interior of the air duct. Air flowing through that duct will be irradiated with UV radiation which will have a germicidal or bactericidal affect on the moving air thereby reducing the impurities in the air flow. Ultraviolet (UV) radiation is considered a viable process for disinfecting drinking water and wastewater in large-scale water treatment systems because it is an effective means of inactivating pathogens, including bacteria, viruses and protozoa, such as Cryptosporidium parvum and Giardia lamblia, and it does not create significant disinfection byproducts. Ultraviolet lamps are widely used by geologists, rockhounds, and collectors of minerals both for identification of mineral materials and for creating the spectacular displays of fluorescence that many minerals emit when illuminated with ultraviolet light. In the fields of molecular biology and biochemistry, ultraviolet light of various wavelengths is used to illuminate, on a transilluminator, electrophoresis gels which are used in the analysis of DNA and proteins. Ultraviolet radiation has long been known to have a number of positive medical benefits, including highly effective germicidal properties. The need for effective germicidal measures in the medical field is always present, in particular for orthopedic surgical procedures which expose vulnerable bone tissue to the air. Ultraviolet lamps are also used in other applications such as forensics, where an ability to change readily between different ultraviolet and visible wavelengths of illumination, in a durable, less expensive apparatus, would also be desirable. UV lamp systems are used in high speed manufacturing processes to cure inks, coatings, and adhesives in a variety of applications. These applications may include, for instance, decorating, laminating, hard-coat protection, circuit board conformal coatings, and printing. UV lamp systems are also used to manufacture silicon semi-conductor wafers. The sterilizing and bactericide action of ultraviolet radiation is used not only for the disinfection of public and private premises, particularly hospitals and nursing homes, but even in rooms opened to the public and also in homes for hygienic and prevention purposes.

A typical ultraviolet (UV) lamp system includes an irradiator to produce high intensity UV light, a power supply to provide electrical power to the irradiator, and an interconnecting high voltage cable. UV lamp systems may be either microwave power UV lamp systems or medium pressure mercury vapor arc lamp systems. One of the commonest sources of ultraviolet light is the low pressure mercury vapor discharge lamp. In this type of lamp, electrical current passes through an essentially evacuated quartz or glass tube which contains small quantities of vaporized mercury metal plus small amounts of an inert "starter" gas. The effect of this electric current is to electronically excite the mercury atoms in such as way as to cause the emission of ultraviolet light of wavelengths characteristic for mercury vapor at low pressure, most notably ultraviolet light of wavelength 254 nm in the UV C wavelength band. Ultraviolet lamp systems, such as those used in the heating or curing of adhesives, sealants, inks or other coatings for example, are designed for coupling microwave energy to an electrodeless lamp, such as an ultraviolet (UV) plasma lamp bulb mounted within a microwave chamber of the lamp system. The microwave power UV lamp system has an irradiator that is equipped with one or more magnetrons. The magnetrons are coupled to the microwave chamber through waveguides that include output ports connected to an upper end of the chamber. The magnetrons convert the electrical power received from the power supply to radio frequency (RF) energy at approximately 2450 MHz. The microwave energy produced by the magnetrons in the irradiator is guided into a cavity which is captivated by an RF screen. An electrodeless medium pressure mercury-vapor lamp is positioned inside of this cavity. In ultraviolet lamp heating and curing applications, one or more magnetrons are typically provided in the lamp system to couple microwave radiation to the plasma lamp bulb within the microwave chamber. For UV curing applications, the bulb is typically formed in the shape of a tube with a slight "hour-glass" shape, and is constructed of quartz. For imaging and semi-conductor applications the bulb is typically spherical. The bulb may be filled with mercury, argon, and/or metal halides such as iron and gallium. The fill inside of the bulbs may absorb the microwave (RF) energy and, consequently, change to a plasma state. The plasma produces radiation energy in the UV lamp system which is the form of UV, visible, and infrared energy. Ultraviolet fluorescent lamps are often used in museum and other displays where powerful lighting is required to properly irradiate and display fluorescent mineral specimens. Fluorescent lamps are used with special ultraviolet filters that transmit the ultraviolet light and absorb the visible light that is generated by the lamps.

A typical ultraviolet lamp system includes a housing to which an ultraviolet lamp is detachably mounted by a pair of oppositely disposed holders. The holders receive and secure the ends of the ultraviolet lamp to the housing. In some UV lamp systems, each holder is connected to a source of electricity for energizing the ultraviolet lamp or bulb. UV lamps are typically installed or mounted in the air ducts of air conditioning (AC) systems in such a manner that the UV light emitted by the lamp floods the interior of the air duct. Air flowing through that duct will be irradiated with UV radiation which will have a germicidal or bactericidal affect on the moving air thereby reducing the impurities in the air flow. Usually, an apparatus for treating water includes a water tank for collecting water including harmful ingredients. An ultraviolet ray lamp is arranged in proximity to the water and irradiates ultraviolet rays into the water in order to remove or decompose harmful contaminants. Ultraviolet light systems used in curing or heating of adhesives, sealants, inks or coatings, for example, include a reflector mounted within or that forms a part of the microwave chamber in which the plasma bulb is positioned. The reflector is an optical element operable to direct the reflected radiation in a predetermined pattern toward the substrate. The ability of a UV light source to disinfect an object is primarily a function of exposure time and intensity of the exposure. For purposes of disinfecting or sanitizing a targeted object, it is therefore advantageous to use a source of UV light that consumes a minimum amount of power, yet produces an intense UV light output.

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