Frequently Asked Questions about UVC

The effectiveness of UVC light is based on the variables of time (length of exposure), intensity of the source (how "intense" the "light" is), and distance (how far the source is from the target). In addition, because different microorganisms require various levels of UVC for inactivation, there is not one answer on how long it may take to inactivate bacteria, as it comes down how the bacterial cell is built. The good news is bacteria and viruses are very susceptible to UVC energy, especially when compared to a spore former like C-diff.

American Ultraviolet is aware of the complexity of the answer to the length of time needed to inactivate bacteria, we take the guess work out of it for our clients by taking into account all variables and delivering a calculated dose of energy directly to the target surface. Our ARTZ 2.0® unit, for example, allows the user to specify the type of microorganism, and the disinfection zone; while our UVC Fixed Mount packages allow the user to select the length of the disinfection cycle needed 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 personal protective equipment PPE, yes. UVC is completely safe when the eyes and skin are correctly protected. Without PPE, prolonged, direct exposure to UVC light can cause temporary skin redness and eye irritation.

No, the products manufactured by American Ultraviolet are not intended to be used for direct human exposure. The International Ultraviolet Association (IUVA) is an 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. We strongly recommend that anyone using UV light to disinfect equipment, surfaces, or air, follow all recommended health and safety precautions and to avoid direct exposure to UV light.

In summary:

  • UV-C radiation of skin, eyes, or any body part should be avoided.
  • 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.
Yes - germicidal UVC lamps have been shown to inactivate most viruses, 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 the majority of microorganisms. The inverse square law applies to germicidal ultraviolet energy as it does to visible light: the intensity decreases as the distance from the lamps increases. The average bacteria will be inactivated in seconds or minutes depending on the intensity and proximity of the source.

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 the majority of microorganisms. The inverse square law applies to germicidal ultraviolet energy as it does to visible light: the intensity decreases as the distance from the lamps increases. The average bacteria will be inactivated in seconds or minutes depending on the intensity and proximity of the source.
Prolonged, direct exposure to UVC light can cause temporary skin redness and eye irritation. American Ultraviolet systems are designed with safety in mind and, when properly installed, 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. These are typically temporary effects and do not 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 disinfects only what it "sees." If you have a Upper Room disinfection fixture, 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 can be a complex calculation but there are some general “rules of thumb” that can be used to estimate the number of fixtures the wattage of the lamp can sometimes be used to generate an estimate. Example: A 15-watt lamp will cover approximately 100 square feet; a 30-watt lamp will cover approximately 200 square feet. This method does not take into account the fixture efficiency so a final layout or design should be performed by a professional.

Germicidal UVC lamps can be used in wall or ceiling-mounted fixtures suspended above the occupied space in a room, or within air ducts of re-circulating systems. The first method is called Upper Air Irradiation. The fixtures are designed so that the energy is directed only upwards toward the ceiling and out the sides. These upper-room germicidal fixtures are mounted at least 7.5 ft. above the floor so occupants are not exposed.

The second method of air disinfection uses UVC lamps placed inside the ventilation system ducts. If a ceiling is too low for an upper-room fixture, this type of an in-duct germicidal fixture can be used. Since the energy is contained in the duct, very high levels of UVC can be used.

In Upper Room air disinfection applications indirect fixtures such as TB and Corner Mount fixtures are hung in the upper portion of the space with the energy contained in the unoccupied space. Only the upper portion of the space is irradiated and persons or animals occupying the area receive no direct exposure. Direct ultraviolet fixtures, such as American Ultraviolet's Utility Fixtures or Deluxe Surface Mounted Fixtures, flood the entire room. In such installations, personnel should not be present or they should be protected by wearing proper PPE, such as American Ultraviolet's Ultra-Shield Face Shields designed for eye and face protection from ultraviolet exposure.


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 disinfection 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.

The level of disinfection 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 (expressed in microwatts per square centimeter) multiplied by exposure time.. The necessary dosage for most common mold spores are listed in the table below. Mold spores are generally much more difficult to damage than microorganisms and viruses and, thus, require a much higher dosage of ultraviolet light. The energy values shown under the percentage are in microwatts per square centimeter of UVC energy.

MOLD SPORES Color 90% 99.9%
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, one 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. 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 17,000 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 17,000 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. These lamps don't lose as much germicidal energy when temperatures fall within the HVAC system, enabling them to inactivate 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 outlive the lamps)
  • Feature 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

> Why UVC for Healthcare Environments
> Why American Ultraviolet Solutions for Healthcare Environments

Visit the Disinfection Update E-newsletter archives (which begin with March 2020) to read helpful stories about the effectiveness of UVC Disinfection.

None of the American Ultraviolet UVC products detailed above are certified, or approved under any applicable laws, as a medical device, and as such, American Ultraviolet, and its Representatives and Distributors, do not currently intend for them to be used as medical devices anywhere globally. Products have not been evaluated by the FDA.