Like a resistor, the voltage across the lamp depends on current flow, but unlike a resistor whose voltage rises with increasing current, the lamp voltage falls with increasing current. The lamps are not designated by voltage (like an incandescent lamp); rather, they are designated by operating current. There are no 120V-rated germicidal lamps, but there are 425 mA-rated lamps that run at 120 V primary. The operating voltage of a germicidal lamp is determined by both the design of the lamp as well as the ballast.

In order to meet various customers’ needs, new lamp platforms have been developed to provide higher ultraviolet power levels in either the same or smaller packages. However, high-power density lamps are less efficient than lower powered lamps.

Yes, the LightSources Group has been successfully providing UV lamps for radiation of harmful organisms in ship ballast water for over a decade.

There are three methods typically employed to treat ship ballast water and they are mechanical (e.g.separation; filtration), physical (e.g. ozone; UV radiation) or chemical (biocides; chlorination).

Yes, UV light can be used in air cleaning systems by eliminating and reducing the VOCs and industrial exhausts containing solvents associated with industrial processes.

Only in high doses. UVC radiation will cause a sunburn and eye discomfort, although it does not penetrate the skin as deeply as UVB rays.

Yes. UVC lamps operating at 254nm can effectively break down ozone.

Yes. Ozone (185nm) produced by certain types of UVC lamps can prevent and destroy chloramines by breaking down the N-CL bonds and also by forming oxidizing hydroxyl radicals.

The answer depends on the lamp type.

  • Cold Cathode lamps unaffected by frequency of starting.
  • Slimline lamps are affected by the number of starts. More starts equals a short lamp life.
  • Hot Cathodes are affect by frequent starts/stops. They will reduce the lamp’s operating life.

Yes. Germicidal UV lamps kill up to 99.9% of most viruses, airborne bacteria and mold spores.

Germicidal UV lamps can be used in Upper Air Irradiation, where the lamps are placed in ceiling fixtures suspended at least 7 feet above the floor so that people will not bump into them or look directly at them. The fixtures are shielded on the bottom.  Otherwise, the lamps are installed in HVAC systems.  UV technology is a  safe and effective solution to disinfect air by removing toxins and harmful pollution caused by many industries.

UV lamps should be cleaned periodically with a dry cotton cloth or paper towel. Never touch the lamp directly – wear rubber gloves and clean with oil-free alcohol only.

UVC radiation does not penetrate tissue deeply. You can protect yourself with clothing and sunscreen and by wearing protective safety glasses.

Germicidal UVC systems work by irradiating flowing water using UVC light. The lamps are placed in a treatment chamber, disinfecting the water within seconds. A dosage of 30 mJ/cm2 is more than sufficient to destroy most water-borne microorganisms.

The mercury arc produces a much weaker line at the wavelength of 185nm. This emission is not directly harmful to micro-organisms, but it is capable of producing ozone, O3, an allotrope of oxygen, in air. Ozone is extremely active chemically and will destroy micro-organisms and VOC’s and act as a deodorizer. An advantage is that it can be carried by air to places that the UV rays cannot reach directly. Lamp ozone production depends upon the type of quartz used. Voltarc lamps designated “L” use ozone-free quartz and produce no ozone, while lamps designated “VH” have a very high ozone-producing output due to the nature of the quartz used.

Germicidal Action Spectrum

Ultraviolet (UV) output emission having wavelengths in the spectral region 100 – 400 nmis extremely effective in killing micro-organisms such as germs, bacteria, viruses and molds. The UVC light is absorbed by the organism’s nucleic acids to create sterility, making it incapable of multiplying to infectious numbers.  A cell that cannot reproduce is considered dead since it is unable to multiply to infectious numbers within a host.

Lamps radiating in this ultraviolet region have been used with great success for air and water purification, protection of food and beverages, sewage treatment and similar applications.

The most effective means of producing UV energy is through the use of a low-pressure mercury arc in which the mercury atoms are excited to a high energy level. Upon dropping back to a low energy, the atoms strongly radiate a characteristic spectral line having a wavelength of 254nm. By a fortunate coincidence, this wavelength is close to 265nm, the wavelength most deadly to micro-organisms.

The heat generated by a germicidal lamp is similar to that generated by a fluorescent lamp of comparable wattage.

Generally, lamps should be replaced at least once a year. Even if the lamp remains lit for many years, the germicidal effectiveness diminishes after about 13,000 hours.

Ozone destroys microorganisms and VOC’s on contact and it is an effective deodorizer.  It can be carried by air into places that UV radiation cannot reach.

High output germicidal lamps (HO lamps) operate between 600 mA and 800 mA. T5 or T6 configuration (15mm or 19mm OD) is available.  Its output is approximately two times that of standard germicidal lamps. It is available in the same lengths as standard germicidal lamps. Its UVC output is related to ambient temperature.

Low pressure amalgam lamps offer three to four times higher power density than other lamp types. They are designed for stable operation over wide ambient temperature range (4°C – 40°C). They are the preferred lamp choice for long-term applications with low or no cycles and they are usable in universal orientation applications.

Soft-glass germicidal lamps operate at 180 mA to 425 mA. Configurations available include T4, T5, T6, and T8 (13, 15 or 19 or 25mm OD). They have a lower UVC output than quartz germicidal lamps. The UVC output is related to ambient temperature. With soft glass, automated lamp production is possible and there are several commercial ballast available for operation. Soft-glass lamps are available in compact fluorescent (CFL) configurations.-term applications with low or no cycles and they are usable in universal orientation applications.

Standard quartz germicidal lamps have the oldest and most established design, with standard lengths and power established by history. They operate at 425mA. These lamps offer the best electrical efficiency (Up to 40% of electrical power is converted to UV). Their warm-up time is approximately 30 – 60 seconds and their UVC output is related ambient temperature. The ambient temperature cannot exceed 40 °C/104°F.

Soft glass naturally transmits at 254nm (no 185nm transmission). Its transmission is lower than quartz glass, its useful life is lower than quartz and it cost less. Learn more about the different glass types on our glass factory page!

Spot amalgam lamps have mercury amalgam applied on the inner surface of lamp. Pellet amalgam lamps have mercury amalgam applied outside of the lamp arc. The use of amalgam allows higher lamp current (1 – 10A) and power ranges from 200W to 1000W. The amalgam composition controls the mercury vapor pressure.  The lamp designs contain more robust filaments to withstand higher current operations. Warm up time is between 3 – 5 minutes.


  • quartz
  • soft glass

Mercury (a small amount necessary to provide the ultraviolet radiation):

  • liquid (20 to 100mg per lamp)
  • solid – pellet (less than 10mg per lamp)
  • spot amalgam (approximately 50mg per lamp)
  • pellet amalgam ( less than 10mg per lamp)


  • filament (Standard = Nominal 425mA; High Output = Nominal 600 – 800mA; Amalgam Lamp = Nominal 1.0 – 10.0 A)
  • special construction

Fill Gas:

  • argon (used for standard 425mA lamps)
  • argon/neon (allows for operation at higher current and voltage)
  • special rare gas mixes


  • standard design
  • custom design (proprietary and patent protection)
  • patent solutions

Instant start:
There is no filament heating applied before starting. These lamps start without any delay but need a higher starting voltage. Instant start lamps are not suitable to switching lamps on and off frequently.

Rapid start:
A short time preheat is applied (1-2 sec) by a capacitor connected parallel with the lamp. They are a low cost solution to increase lamp life.

Preheat start:
An individual filament preheat circuit is applied for as long as necessary to initiate arc flow at the established open circuit start voltage.  They are an expensive solution to increasing lamp life, but are a must for multi-cycle applications.

Standard Lamps
Applications where flow rates are lower and exposure time can be longer.

HO Lamps
Applications where higher flow rates or dosages are required while maintaining a limited footprint.

Amalgam Lamps
Applications where very high output is required and/or ambient temperature is an issue.

Characteristic Comparison of Germicidal Lamp Types

CharacteristicLP (Quartz)LP (Softglass)LP AmalgamMP
Emission185 + 254nm254nm185+254nmpolychromatic
Gas Vapor Pressure1 – 10 mbar1 – 10 mbar1 – 10 mbar1 – 5 bar
Hg OperatingTemperatures30-50°C30-50°C90-120°C600-800°C
Arc Length5 – 155cm7- 148cm27-200cm5-150cm
Lifetime (hours)9,000*9,000*13,000**3,000 – 5,000
Germicidal Efficiency(200-300nm)30 – 40%30%30 – 35%12 – 16%
Power Densitiy (W/cm)0.3 – 0.50.25 – 0.31.0 – 2.050 – 250
Influence of AmbientTemperaturesHIGHVERY HIGHLOWNEGLIGIBLE
* 13,000h with LongLife Coating
** 16,000h with LongLife Coating

Doped quartz for low ozone producing applications. Doping blocks 185nm transmission.

Fused (natural) quartz (un-doped) for very high ozone producing applications. Quartz transmits both 185 and 254nm radiation.

Synthetic fused quartz for very high ozone producing applications. Better transmittance at 185nm but at significantly higher cost.

Electromagnetic Ballast: 

  • Pros: They have a low cost and are reliable and robust.
  • Cons: They have a high power consumption and a larger dimension.

Electronic Ballast:

  • Pros: They have a low power consumption and 10% higher efficiency. There is no lamp voltage limitation and they have a low weight.
  • Cons: They have a higher cost.

The standard base types include four-pin circle base, miniature bipin, medium pin, slimline single pin.

General FAQs 1

A ballast serves two purposes. One, it provides enough voltage to break down the rare gas contained in the lamp, and two, it limits the current flow through the lamp. For some lamps, the ballast also needs to provide heat to the electrodes at the lamp ends (preheat). Did you know Light Sources and LightTech offer an extensive line of electronic ballasts? Check the specs on our electronic ballast page.

  • Lamp Design
  • Ambient temperature: temperature of gas or liquid around lamp
  • Thermal conductivity of medium
  • Dimming range
  • Age of lamp
  • Operating frequency of ballast
  • Frequency of on / off cycles

Ballasts are mostly a conductive metal coil which can be designed for low frequency operation (50 – 60 Hz) or high frequency operation (10 – 100 kHz). The coil is more efficient than the resistance because the heat loss is smaller. High frequency operation needs a smaller coil for the same impedance as low frequency operation.

Did you know Light Sources and LightTech offer an extensive line of electronic ballasts, covering a wide range of UVC germicidal lamps.

Germicidal lamps are low-pressure, mercury/rare gas discharge devices similar to fluorescent lamps. This is true in both operation and construction except for the lack of a phosphor coating on the inner lamp wall.  A UV germicidal bulb converts electricity into ultraviolet radiation and the energy that is generated in the UV spectrum is used to destroy bacteria, fungi and viruses (microorganisms).

The features of a germicidal lamp include:

  • The envelope has high transmittance for 254nm radiation
  • A UV lamp that emits a significant portion of its radiative power in the UV-C Band (100 to 280nm)
  • An ozone producing UV lamp that produces UV energy of wavelengths shorter than 220nm that decomposes oxygen, O² , producing ozone, O³.
  • A UV lamp that generates energy at 185nm which is particularly effective in producing ozone.

The lamp body may be made of pure fused quartz that will transmit both 254 and 185nm radiation (VH glass), quartz with Titanium added to block out most of the 185nm radiation (L glass), or of a “soft” glass formulated to transmit 254nm Electrode radiation (L glass).

Low-frequency lamps need a starter to ensure the preheat current for the filament. After warming, the starter turns off the current and the starting voltage is generated by the coil, beginning the discharge.

Because the lamp has warmed does not mean that the output has stabilized.  On first lighting after installation, mercury may be partially distributed throughout the lamp as randomly sized drops in equally random locations.  As the lamp operates, mercury will evaporate from its initial locations and the vapor pressure increases until it reaches a constant level. The mercury either condenses in the coldest part of the lamp (which controls the vapor pressure) or it is absorbed into the amalgam (if present).

Before the lamp is turned, on mercury vapor pressure within it is determined by ambient temperature, and is essentially zero.  At ambient temperatures below 20° C, mercury vapor pressure is below 1 micron.  When the lamp is turned on and power is dissipated in a positive column, the lamp body begins to heat raising vapor pressure to 6 microns needed, which is needed for maximum output. Depending on the lamp design, operating current, and the environment, this time can be as short as 1 minute or as long as 30 minutes.  In most cases the lamp will warm up in 5 minutes.

CharacteristicLP (Quartz)LP (Softglass)LP AmalgamMP
Emission185 + 254nm254nm185+254nmpolychromatic
Gas Vapor Pressure1 – 10 mbar1 – 10 mbar1 – 10 mbar1 – 5 bar
Hg OperatingTemperatures30-50°C30-50°C90-120°C600-800°C
Arc Length5 – 155cm7- 148cm27-200cm5-150cm
Lifetime (hours)9,000*9,000*13,000**3,000 – 5,000
Germicidal Efficiency(200-300nm)30 – 40%30%30 – 35%12 – 16%
Power Densitiy (W/cm)0.3 – 0.50.25 – 0.31.0 – 2.050 – 250
Influence of AmbientTemperaturesHIGHVERY HIGHLOWNEGLIGIBLE
* 13,000h with LongLife Coating
** 16,000h with LongLife Coating

Over time, all germicidal lamps lose their output intensity until they reach such an output level that they are considered to be no longer effective in their application. The graph illustrates the gradual depreciation of initial lamp UV output. Our lamps have a general lamp life of 13,000* operating hours.

Approximate UV Fall-Off with Time

* 16,000 hrs. with proprietary long-life coating

During operation, a lamp may be 25º C/77 º F or more above ambient over most of its surface. The lamp will produce its maximum output when the mercury vapor pressure is approximately 6 microns (.006 Torr or about 8 millionths of one atmosphere). This is the pressure over liquid mercury at a temperature of 45º C/ 113º F.

When a germicidal UVC system is used to irradiate an entire room, such as a surgical suite, personnel should wear eye goggles or face shields designed for ultraviolet exposure, and by covering as much skin as possible with clothing or sunblock.

Germicidal UVC technology is used in many industries worldwide for water, air, and surface treatment, including UV curing. Markets include:

UV radiation at 185nm produces ozone, which is active oxygen. Ozone is one of the most effective natural bactericides and can kill almost every form of virus. Radiation at 254nm is an effective sanitizer, even oxidizing body oil, urine, perspiration, fecal matter, and cosmetics. It can prevent and destroy chloramines by breaking down the N-CL bonds and by forming oxidizing hydroxyl radicals.  At the 254nm wavelength, UVC is absorbed by the organism’s DNA, eliminating its ability to reproduce.

The discharge lamp cannot work without current limitation. After start, it would fail shortly because lamp current begins to increase rapidly.

Environmentally Friendly
UV radiation is environmentally friendly, sterilizing without the use of chemicals; toxic chemicals require specialized storage and handling; without chemical usage, there is no concern of overdosing or process by-products.

Cost Effective
UV technology has a low initial capital cost and offers reduced operating costs.

Efficient and Effective
UV radiation offers an immediate treatment process with no requirement for holding tanks or long retention/exposure times.

UV radiation is highly compatible with other water and air treatment processes while not introducing changes in taste, odor, Ph, conductivity or chemical properties of the air/water in which it is used.

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