Frequently asked questions

What is UV-C?

Ultraviolet (UV-C) – refers to short-wavelength ultraviolet radiant energy that has been shown to kill bacteria and to inactivate viruses. Wavelengths in the ultraviolet band known as the “UV-C” (from 200 to 280nm), have been shown to be the most effective for disinfection.

Is UV-C new technology?

No. UV-C has been used since the 1930's to clean air, water, and surfaces. Primarily used in hospital and surgery suites, these solutions are not available for commercial use.

How does UV-C work to inactivate a virus?

On a microscopic level, individual, UV-C photons interact with the RNA and DNA molecules in viruses and bacteria to render them non-infectious.

In lighting we have lumens as measurement, how is UV-C effectiveness measured?

UV-C effectiveness is proportional to the exposure dose (radiant exposure, typically in millijoules* per square centimeter, mJ/cm2, or joules per square meter, J/m2), which is the product of the radiant power (irradiance, typically in mW/cm2 or W/m2) and time (from 1 μs to several hours).

How much dosing is required for eliminating a pathogen?

UV-C effectiveness is usually measured on a log-scale, which is linearly associated with dose. For instance, if 1 mJ/cm2 UVGI (Ultraviolet germicidal Irradiance) achieves a 1-log (10-fold) killing rate, then 4 mJ/cm2 would achieve a 4-log (10,000-fold) killing rate. The 4-log rate is commonly referred to as 99.99%. If a certain UV exposure kills 90% of a bacterial population (frequently referred to as "one-log kill"), doubling the exposure time or intensity can kill only 90% of the residual 10%, for an overall germicidal efficacy of 99% ("two-log kill"). To be effective in practice, achieving two log-kills (99% inactivation) is frequently accepted.

How do we know it works and in particular for viruses?

All known micro-organism is susceptible to UV-C. Bacteria, mold and fungi will be killed, and viruses will be inactivated. It is only a matter of how much time and how much radiant power is provided. (Source: 1 Fluence (UV Dose) Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa, Viruses and Algae Revised, updated and expanded by Adel Haji) The dose required to achieve 1-log killing is often called the D90-value (where 90% of the pathogen is killed), and these values have been empirically determined for many pathogens and microorganisms. (Source: Kowalski -2017) UV-C has been demonstrated to work very effectively to inactivate viruses including coronaviruses. (Source: Darnell et al. – 2004 showed that UVC exposure resulted in >5 log reduction of SARS-CoV.)

Will UV-C work on the SARS-CoV-2 (COVID-19)?

The National Emerging Infectious Diseases Lab at Boston University conducted research to confirm the effectiveness of Signify’s UV-C sources in inactivating SARS-CoV-2, the virus that causes Covid-19. The research team identified that a dose of 22mJ/cm2 will result in a reduction of 99.99% of SARS-CoV-2. (Source: Signify Press Release)

Are UV-C cleaning solutions safe?

UV-C poses a health hazard to the eyes and skin if the lamps are improperly used or installed. Products have been developed with a UL8802 Safety Certified UV-C System designed to meet new UL 1598 standards.

If these are not "light" then how do you know it is on?

Like odor added to natural gas, the UV-C source does have some emission that is visible so that you can see when it is on. These products are blue when on.

Does surface UV-C solutions replace the need for cleaning?

No. While UV-C has been shown to be excellent for cleaning surfaces, it does not penetrate surfaces and cannot clean dirty surfaces. The inability of the UV radiant energy to reach shadowed recesses of surfaces or to penetrate dust and other matter may negatively affect cleaning. For these reasons, UV-C is typically used as a supplement to other cleaning processes. “Enforcement Policy for Sterilizers, Disinfectant Devices, and Air Purifiers During the Coronavirus Disease 2019 (COVID-19) Public Health Emergency Guidance for Industry and Food and Drug Administration Staff”. (Source:

I have heard these need to be EPA approved, what does that mean?

UV-C devices are officially listed as pesticide devices. As such, pesticides production facilities must be registered with the EPA. All of our product are registered and comply with these regulations.

How do we determine the number of sources and energy required to effectively clean an area?

Similiar to light energy, we have tested IES files that provide the irradiance and the electrical power needed to operate each fixture. Similiar to lighting layouts, we can translate this into power delivered to an area in the same manner we calculate foot candles. The power can be translated to the time needed to eliminate a pathogen based on its “dose”. This time is typically planned for elimination of 99.99% from the surfaces. In many cases the “4-log kill” is accomplished in minutes.

Do the UV-C Upper Room Unit move air in the space where installed?

No, they do not. They take advantage of the natural air flow in the room due to convection, people moving in the space, as well as the HVAC system.

What is Air Changes per Hour (ACH) and what does it have to do with upper air fixtures if they don’t move the air?

Air Change per Hour (ACH) is a measure of how many times the air within a defined space is replaced. Indoor Air Quality (IAQ) can directly improve by increasing the ACH with an HVAC system. Most commercial applications deliver 3-4 ACH. Recommendations from CDC are to deliver 6–10 ACH for optimal IAQ. With an HVAC system, 6 ACH is considered uncomfortable and above 10 is loud and windy. Our fixtures disinfect the air and increase the effective ACH (eACH) in a space without increasing the air flow in the room. Using these products, the eACH can reach up to 18, which has demonstrated 80% reduction in the spread of tuberculosis. [1] Mphahlele.M. et al (2015) Institutional Tuberculosis Transmission: Controlled trial of upper room ultraviolet air disinfection – A basis for new dosing guideline. [2] Interpolated data. [3] Adapted from CDC (1994). Guidelines for preventing the transmission of Mycobacterium tuberculosis in health care facilities. MMWR 1994; 43 (RR- 13): 1-32.

Are UV-C Upper Air solutions safe?

Exposure to UV-C can cause temporary skin irritation (think sunburn) or eye irritation (think welder’s eye or mild eye sunburn). Our UV-C Upper Air products are optically designed to control the UV-C irradiance and ensure it remains in the space above the occupants. UL 1598 annex L requires the installation to confirm.

Can people be in the room when the UV-C Upper Room products are on?

Absolutely. These products are designed for continuous use in an occupied space.