Frequently Asked Questions about UVC

It is believed that COVID-19 is an enveloped virus with a single positive-stranded RNA genome. Coronaviruses have an envelope composed of a lipid bilayer, proteins, and sugars with a protein capsid. At this point American Ultraviolet does not believe that any testing of this particular strain has been performed. However, several coronaviruses similar in construction have been found to be susceptible to UVC energy - Learn more.

The short answer is - minutes - however, it is a little more complicated than that. The effectiveness of UVC light is based on the variables of time (length of exposure), intensity of the source (how "bright" the "light" is), and distance (how far the source is from the target). In addition, because different pathogens require different levels of UVC to deactivate them, there is not one answer about how long it takes to kill all bacteria, as it also comes down to the way the cell is built for each type of bacteria. The good news is bacteria, and viruses, are very susceptible to UVC energy, especially when compared to a spore former, like C-diff.

Because American Ultraviolet is aware of the complexity of the answer to the length of time needed to "kill bacteria," we take the guess work out of it for our clients by taking into account all of these variables, and delivering a calculated dose of energy directly to the target. Our ARTZ 2.0® unit, for example, allows the user to specify the type of pathogen, and the disinfection zone; while our UVC OR package allows the user to select the length of the disinfection cycle needed to target specific pathogens without having to do the math.

UV technically doesn't "kill" bacteria, but rather it inhibits replication, or sterilizes it, by destroying the DNA. A more detailed explanation is that the UVC energy is absorbed by the DNA and RNA contained in the cells, and this creates dimers or a "double bond" between adjacent nucleotides (i.e. thymine). The formation of these dimers is what inhibits the ability of the chain to replicate, which in turn leads to the death of the colony.
With proper PPE, yes. UVC is completely safe when the eyes and skin are protected. Without any PPE, prolonged, direct exposure to UVC light can cause temporary skin redness and eye irritation, but does not cause skin cancer or cataracts.

Recent reports suggest that ultraviolet (UV) light can be used on the human body to disinfect against the coronavirus. The International Ultraviolet Association (IUVA) and RadTech North America are educational and advocacy organizations consisting of UV equipment vendors, scientists, engineers, consultants, and members of the medical profession. We would like to inform the public that there are no protocols to advise or to permit the safe use of UV light directly on the human body at the wavelengths and exposures proven to efficiently kill viruses such as SARS-CoV-2. UV light under the conditions known to kill such viruses are also known to cause severe skin burns, skin cancer, and eye damage. We strongly recommend that anyone using UV light to disinfect medical equipment, surfaces, or air in the context of COVID-19, applications that are supported by sound scientific evidence, follow all recommended health and safety precautions and to avoid direct exposure of the body to the UV light.

Additional Information on UV Technology for Disinfection:

The ultraviolet spectrum is a band of electromagnetic radiation at higher energies than visiblelight, split into four major categories: UV-A (400 – 315 nm), UV-B (315 – 280 nm), UV-C (280 – 200 nm), and vacuum-UV (VUV, 100 – 200 nm). UV-A and UV-B are present in sunlight at the earth's surface; these parts of the ultraviolet spectrum are common causes of sunburn and, with longer-term exposure, melanoma. The risks of human exposure to UV-A and UV-B are well known. Solar UV may be used for disinfection purposes; exposures in the order of several hours to days might be effective at treating surfaces and water. Artificial sources of UV-A and UV-B are not commonly used for disinfection. UV-C has been used for disinfection for over a century, with applications in water treatment, air systems, and surfaces. The use of UV-C as a disinfectant is supported by decades of scientific research. UV-C radiation is absorbed by DNA and RNA (the genetic code for all lifeforms), changing its structure. This damage inhibits the ability of the affected cells to reproduce, meaning that they cannot infect and are no longer dangerous. Whereas the UV exposure required to inactivate different microorganisms varies, though there are no known microorganisms that are immune to this treatment and it is regularly used against bacteria, viruses, and protozoa.

In the same way that UV-C can inactivate bacteria and viruses, it can be damaging to human cells too, since our cells also contain DNA. This exposure can cause skin irritation, damage to the cornea, and cell mutations leading to cancer. Exposure to UV-C radiation is regulated globally, with a common agreement on the risk to human health and safe exposure levels. These regulations and standards set limits on allowable exposure, though in all cases it is recommended to avoid UV exposure where possible.

In summary:

  • UV-C irradiation of the skin, eyes, or any body part should be avoided wherever
  • Always wear appropriate PPE when handling un-shielded UV-C radiation sources (e.g.
    long-sleeved clothing, gloves, and a UV-opaque face shield).
  • Always use UV-C devices in accordance with the manufacturer's operating instructions
    to ensure safe operation, and within appropriate enclosures where light leakage has
    been controlled, and where the risks have been properly managed.
Yes -germicidal UVC lamps kill up to 99.9% of most viruses, airborne bacteria and mold spores.
Germicidal UVC lamps from American Ultraviolet are good for approximately 17,000 hours (two years) of continuous use, with only 20% decrease in output over the two years.
The exposure of germicidal ultraviolet is the product of time and intensity. High intensities for a short period and low intensities for a long period are fundamentally equal in lethal action on bacteria. The inverse square law applies to germicidal ultraviolet as it does to light: the killing power decreases as the distance from the lamps increases. The average bacterium will be killed in ten seconds at a distance of six inches from the lamp in an American Ultraviolet Germicidal Fixture.

There are three common types of germicidal UVC lamps:

    "Cold Cathode" lamps are instant-start, using a large cylindrical cathode instead of a coil filament, so lamps have a long life that is unaffected by frequency of starting.

  1. "Slimline" lamps, are also instant-start and are available in low-, high- and very high-ozone types. Their lamp life is governed by the electrode life and number of starts. Because of their high initial UVC emission, and good maintenance, Slimline UVC Germicidal Lamps are well adapted for applications such as air cooling and heating systems, conveyor lines, water sterilization and other applications that require "around-the-clock" use and therefore do not need to be turned off.
  2. "Hot Cathode", or preheat/hot cathode, lamps generally use standard, off-the-shelf fluorescent ballasts, providing advantages in economy and space. Preheat lamps have four electrical connections per lamp and require more wiring than instant-start lamps. Frequent starts/stops will reduce the lamp life of Hot Cathode lamps.
Ultraviolet light in the germicidal wavelength - 185-254 nanometers - renders the organisms sterile. When organisms can no longer reproduce, they die. To learn more please visit the Basics of UVC section within the Overview section.
Germicidal UVC lamps do not produce much heat - about the same as fluorescent lamps.
The exposure of germicidal ultraviolet is the product of time and intensity. High intensities for a short period and low intensities for a long period are fundamentally equal in lethal action on bacteria. The inverse square law applies to germicidal ultraviolet as it does to light: the killing power decreases as the distance from the lamps increases. The average bacterium will be killed in ten seconds at a distance of six inches from the lamp in an American Ultraviolet Germicidal Fixture.
Prolonged, direct exposure to UVC light can cause temporary skin redness and eye irritation, but does not cause skin cancer or cataracts. American Ultraviolet systems are designed with safety in mind and, when properly installed by a professional contractor, do not allow exposure to ultraviolet irradiation and allow for safe operation and maintenance. If you are exposed to direct germicidal light, it can burn the top surface of your skin. If your eyes are exposed, it would be similar to a "welder's flash", and your eyes can feel dry or gritty. At no time do germicidal lamps cause any permanent damage.
Long-term exposure of germicidal UVC light to plastics will shorten the shelf life of the plastic by approximately 10%. Example: If the plastic would normally last about ten years, and it's exposed to germicidal UVC light the entire time, it would probably need to be replaced in 9 years. Plant life may be damaged by direct, or reflected, germicidal ultraviolet rays. Transient dyes and colors may be faded from prolonged exposure to ultraviolet rays.
No - germicidal UVC sterilizes only what it comes in contact with. If you have a room sterilizer, such as one of our TB models, and there are light fixtures or fans hanging from the ceiling, the UVC light will stop when it hits these fixtures. This may require additional fixtures placed strategically in the room to ensure complete coverage.
This is determined by the wattage of the lamp. Example: A 15-watt lamp will cover approximately 100 square feet; a 30-watt lamp will cover approximately 200 square feet.

Germicidal UVC lamps can be used in ceiling fixtures suspended above the people in a room, or within air ducts of re-circulating systems. The first method is called Upper Air Irradiation. The fixtures are shielded on the bottom so that the radiation is directed only up toward the ceiling and out the sides. These upper-air germicidal fixtures are mounted at least 7ft. above the floor so that people will not bump into them or look directly at the lamps.

The second method of air disinfection uses UVC lamps placed inside the ventilation system ducts. If a ceiling is too low for an upper-air irradiation fixture, this type of an in-duct germicidal fixture can be used. Also, because people are not exposed to the UVC radiation, very high levels can be used inside the ducts.

In personal protection applications (the use of lamps for room irradiation in homes, schools, offices, etc.), indirect fixtures such as TB and Corner Mount fixtures are mounted above eye level. Only the upper air is irradiated and persons or animals occupying the area receive no direct exposure. Direct ultraviolet irradiations, such as American Ultraviolet's Utility Fixtures or Deluxe Surface Mounted Fixtures, irradiate the air in the entire room. In such installations, personnel should be protected by wearing either goggles or face shields, such as American Ultraviolet's Ultra-Spec 100 Safety Goggles and Ultra-Shield Face Shields designed for ultraviolet exposure, and by covering as much


UVC Is Efficient and Safe

UVC Germicidal Fixtures increase the value of all air conditioning and air-circulating systems by:

  • Maximizing system efficiency
  • Prolonging blower life
  • Providing healthier air to breathe

Treating air that passes through an HVAC unit with ultraviolet light will reduce, or eliminate, DNA-based airborne contaminants (bacteria, viruses, mold spores, yeast, protozoa), and provide much healthier air to breathe. UVC Germicidal Fixtures are a labor-free solution that will not harm occupants, equipment or furnishings because they produce no ozone or secondary contaminants. For more than 70 years, tens of thousands have been safely installed in hospitals, clinics, processing plants, commercial offices, manufacturing sites and other commercial facilities and multi-and single-family residences around the world.

Basics of UVC

For HVAC applications, just as with all other UVC sterilization applications, direct exposure to 254nm UVC radiation, given appropriate exposure time, will inactivate the DNA and RNA of microorganisms (such as bacteria, viruses, mold spores, yeast, and protozoa), rendering them "sterile" (unable to reproduce), which, in biological terms, results in a "dead" microorganism.

An acceptable kill rate is determined by the total amount of UVC energy a microorganism "sees." This is a "dosage." Dosage is a product of the intensity of UVC radiation (expressed in microwatts per square centimeter) and exposure time to that radiation. You can find the necessary dosage for most common mold spores in the following table. Mold spores are generally much more difficult to kill than microorganisms and viruses and, thus, require a much higher dosage of ultraviolet light. The values shown under the percentage kill are in microwatts per square centimeter of UVC energy.

MOLD SPORES Color 90% 90%
Aspergillius flavis Yellowish green 60,000 99,000
Aspergillius glaucus Bluish green 44,000 88,000
Aspergillius niger Black 132,000 330,000
Mucor racemosus A White gray 17,000 352,000
Mucor racemosus B White gray 17,000 352,000
Oospora lactis White 5,000 11,000
Penicillium expansum Olive 3,000 22,000
Penicillium roqueforti Green 13,000 26,400
Penicillium digitatum Olive 44,000 88,000
Rhisopus nigricans Black 111,000 220,000
Germicidal Lamp Technology

When researching UVC Germicidal Fixtures, you may come across several different types of lamp technologies and configurations.

All UVC lamps essentially consist of a quartz envelope containing mercury and other gases and electrodes. When the lamp is struck, the energy between the electrodes excites the mercury into a vapor, which produces C-band ultraviolet energy. Almost all germicidal lamps currently being used in mainstream HVAC applications have been low-pressure lamps; American Ultraviolet recommends using High Output lamps. Following is information about some of the more common UVC lamps:

  • Hot Cathode low-pressure lamps - this older technology, which is not very common today, uses a soft glass envelope (which devitrifies faster) and small electrodes (which put out less intensity and doesn't last as long as other lamps). They are rather inexpensive when compared to Slimline or High Output lamps.
  • Slimline low-pressure lamps- these have been the most commonly used germicidal ultraviolet lamps. They utilize a much harder quartz envelope and bigger electrodes than hot cathode lamps. They can have a useful life of up to 15,000 hours and produce almost two times the intensity of a hot cathode lamp of the same size.
  • High-output lamps- essentially Slimline lamps, these high-output lamps use a heavy-duty electrode and slightly different gas mixture to produce 100% more UV intensity than an equal length Slimline lamp, while still maintaining an effective life of up to 15,000 hours. The majority of American Ultraviolet UVC Germicidal Fixtures for HVAC applications use an even more efficient High Output ultraviolet lamp, and have an effective life of up to 17,000 hours (two years)
American Ultraviolet High Output Lamps

American Ultraviolet Germicidal Fixtures feature the highest High Output (HO) Lamps, which provide even greater efficiency than lamps other companies offer. And these lamps don't lose as much germicidal energy when temperatures fall within the HVAC system, enabling them to kill more mold and bacteria across a wider temperature and air velocity range than all others.

UVC Germicidal Fixtures from American Ultraviolet also:

  • Resist moisture, which prevents corrosion on lamp ends and electrical connections that can shorten lamp life (our fixtures actually outlive the lamps)
  • Feature patent pending lamps that are the easiest to install and replace
  • Contain lamps that offer a two-year guarantee (17,000 hours) of operation with only 20% decrease in output over the two years
  • Offer "Green" lamps that contain ≤ 8mg of mercury
  • Are made, assembled and tested in the USA
  • Can be used in unique custom in-duct and coil installations, for example, when very high volume airflow situations exist
  • Can be ordered with indicator lamps that notify customers when the lamp life has expired
  • Are very easy to maintain - simply wipe down with a damp cloth when performing already scheduled filter cleaning - no additional maintenance is necessary

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