UV Lamps - UV Lamp Types
UVC Production by Germicidal UV Lamps
There are many types of lamps that artificially produce UV. There are UV lamps for tanning, for counterfeit money detection, blacklight stage lamps and lamps for mineral displays, lamps that produce Ozone and germicidal UV lamps. The focus of this document are the germicidal UV lamps, which emit shortwave UV light in the ultraviolet section of the spectrum also known as UVC or germicidal UV. There is more information on the nature of UV in the UV Science Facts section. Here we will discuss the artificial UV production by the different UV lamps and the specs of the different types of UV lamps. Many times people refer to the UV lamps as UV bulbs as in regular light bulb. Even though bulb is not the correct term, replacement bulb, UV bulb or bulbs are widely accepted in the industry as a reference to the UV lamps.
UV Lamps – History and Development
UV is artificially produced by mercury vapor low and medium pressure lamps. The low pressure lamps are most effective, because they emit most of the radiant energy in the germicidal wavelength of 253.7nm also known as the UVC part of the spectrum. This is the reason low pressure lamps are mostly used in germicidal UV applications. These lamps are sometimes called “amalgam” lamps because they contain solid amalgam “spots” (an amalgam is an alloy of mercury with another element, such as indium or gallium) that controls the mercury vapor pressure.
All lamps have secondary emissions, including small amounts of UVA, UVB, visible
light (above 400nm wavelength) and heat. The blue glow of the germicidal UV
lamps is not indicative to the effective germicidal output they produce – that
could be only determined with a properly calibrated UV sensor and monitor.
Types UV Lamps
Cold Cathode Germicidal UV Lamps
The Cold Cathode Germicidal UV Lamps are instant-start lamps with a
cylindrical cold cathode type of electrode. These lamps are available in
different sizes and may be operated either from single lamp transformers or in
series trough the medium of high voltage transformers.
Hot Cathode Germicidal UV Lamps
The Hot Cathode Germicidal UV Lamps are similar in their operation to the standard fluorescent lamps. The Hot Cathode lamp operates from a ballast or transformer and requires a device such as the glow switch starter to preheat the electrodes in order to start the lamp. The electrodes, located at the ends of the lamp, are tungsten filaments coated with emission material and, under normal operation, govern the life of the lamp. In view of the fact that the life of the electrodes is shortened by frequent starts, the lamp life is rated according to the number of times the lamp is started. Operation at refrigerator temperatures may result in excessive lamp blackening and rapid depreciation in ultraviolet output. Starting of the Hot Cathode lamps at low temperature is sometimes unreliable and may require special equipment.
Slimline Germicidal Ultraviolet Lamps
The Slimline Germicidal Ultraviolet Lamp is an instant-start lamp, similar to
the Slimline fluorescent lamp. The Slimline lamps are available in low, high and
very high ozone types. The lamp life is governed by the electrode life and
number of starts.
High Output Germicidal UV Lamps
The most recent addition to the UV lamp line of products is the type of High
Output germicidal UV lamps. The HO lamps are the consequent result of constantly
applied know-how and the latest lamp manufacturing processes. High UV output
over a great temperature spectrum, a long life and good behavioral patterns are
the pointers for the High Output UV lamps. Only high quality raw materials are
used in the lamp production. A fine tuning with the automatic electronic
ballasts guarantees the lowest tolerance and a maximum UV stability.
Light Emitting Diodes (LED) UV Lamps
Recently a completely new technology for UV production started to emerge. This is the UV Light Emitting Diodes or UV LED lamps. The UV LEDs are the next generation UV producing devises that will compete with the established UV lamps. Some researchers claim that the UV LEDs have better characteristics surpassing the regular UV lamps. However at this time there is no UV LED equipment that can compete with the high output UV lamps in real world production conditions.
Lamp Shapes and Lamp Connectors
There are many lamp shapes: cylindrical lamps - like a glass tube, circular tube, multi-coiled tube lamps, U-shaped lamps, double tubes or by-axial lamps. The UV LED lamps are much smaller than the regular lamps and can be installed in spaces that do not permit installation of regular lamps.
All lamps are powered by ballasts that provide the starting electrical voltage to ionize the gas in the UV lamp and then limiting the current to the nominal level. Lamp ballasts can be either magnetic or electronic. The LED UV lamps do not require ballasts for their operation.
The lamps have different types of connectors at one or both ceramic ends. The connectors can be single-pin, double-pin or four-pin. The single and double pin connectors are located on both ends of the lamps, while the four-pin connectors are single connectors at one end of the lamp.
UV Lamps Aging
The decrease in UV lamp output over the typical lifespan of 8,000 - 12,000 hours can vary between 15-40%. The manufacturer should be consulted for information on the end-of-life output of UV lamps. The decrease in UV output should be accounted for in the design phase such that the lamp output does not decrease to a point where the air treatment system becomes ineffective. The most conservative approach is to size the system based on the end-of-life of the lamp UV output. Selecting lamps based on end-of-life UV output will avoid the lamps aging problem.
The lamps should be kept clean and free of dust at all times. If dust accumulates on the lamp it will absorb the UV and convert it to heat, therefore lowering the effectiveness of the UV lamp. Appropriate filtration of the air prior to the UV lamps is recommended.
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