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Germicidal UVC Light Frequently Asked Questions

American Ultraviolet LogoPlease see below our frequently asked questions about Germicidal UVC Light sterilisation. We also welcome phone calls and emails regarding these, and any other questions you may have. For relevant email or phone numbers please visit our Contact Us page.

Do germicidal lamps kill viruses/ mould?

Yes -germicidal UVC lamps kill up to 99.9% of most viruses, airborne bacteria and mould spores and will help prevent future mould growth.

How often do the lamps need to be replaced?

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.

Should UVC lamps be cleaned?

Yes – depending on the surrounding environment, UVC lamps should be checked periodically (approximately every three months), and can be cleaned with a dry cotton cloth or paper towel. Wear rubber gloves and clean with alcohol only. This will also help maximize lamp life.

How much intensity do I need to kill certain organisms?

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.

Can germicidal lamps be turned on and off continuously?

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.
“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.
“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.

How do germicidal lamps kill?

Ultraviolet light in the germicidal wavelength – 185-254 nanometers – renders the organisms sterile. When organisms can no longer reproduce, they die.

How hot do the lamps get?

Germicidal UVC lamps do not produce much heat – about the same as fluorescent lamps.

To be effective, how close to the surface do the lamps need to be?

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 150mm from the lamp in an American Ultraviolet Germicidal Fixture.

Do I need ozone-producing lamps?

It depends on your particular need. Most of the time you do not need ozone, unless there are shaded areas that the UVC light cannot reach. Ozone helps to “carry” the ultraviolet radiation in the air to where it normally cannot reach directly.

When do I need to use ozone-producing lamps?

Germicidal UVC lamps generate energy at 185 nanometers as well as 254nm. This UVC emission produces abundant amounts of ozone in air. Ozone is an extremely active oxidiser and destroys micro organisms on contact. Ozone also acts as a deodoriser. Another advantage is that it can be carried by air into places that UVC radiation cannot reach directly.

What damage will the lamps do to me?

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.

What effects does UV light have on surrounding materials?

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.

Can germicidal UVC penetrate surfaces or substances?

No – germicidal UVC sterilizes only what it comes in contact with. If you have a room steriliser, 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.

How do you determine the square meterage that one germicidal UVC lamp will cover?

This is determined by the wattage of the lamp. Example: A 15-watt lamp will cover approximately 10 square metres; a 30-watt lamp will cover approximately 20 square metres.

Do the lamps need a ballast to work?

Yes – a germicidal lamp is one part of a system, and the system cannot be fully defined and optimized unless the lamp and ballast combination is determined. It is the interaction of the lamp and ballast that is the true determinant of system performance.

How are UVC lamps used to disinfect the air?

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 2.1m 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.

What safety precautions should be taken when using germicidal UVC?

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 skin as possible with clothing or sun block.

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