Since the beginning of the COVID-19 pandemic, Henderson Engineers Director of Engineering Dustin Schafer and many of our technical leaders, including Electrical Technical Director Sean Turner have been fielding questions relating to infection control technologies like UV disinfection. Below are some of the most common questions we’ve received.

What is UV light?

Ultraviolet or UV “light” is electromagnetic radiation with a wavelength shorter than that of visible light, ranging from 100 nm to 400 nm.

What’s the difference between UV and UVc?

The UV wavelength spectrum includes four bands: UVa (315 to 400 nm), UVb (280 to 315 nm), UVc (200 to 280 nm), and UVv (10-200 nm). UVc has been shown to have the greatest impact on inactivating microorganisms and such is the band used in UV disinfection applications.

Isn’t UV dangerous to people or animals?

UVa and UVb are widely known for their harmful effects on human skin and links to skin cancer (exposure to sunlight). However, UVc wavelengths emitted by the sun are absorbed by our atmosphere, keeping their radiation from reaching Earth’s surface. As such, UVc hasn’t been directly linked to harmful outcomes in a non-artificial (natural sunlight) situation. However, direct exposure still isn’t recommended.

The easiest way to protect occupants while still using UVc is to shield them from direct exposure by either aiming the lamp away from them (as in an upper room configuration), locating it away from occupants (as in an in-unit HVAC application), or only operating the device when occupants aren’t present (with occupancy sensors) or during off hours surface cleaning applications.

How does UV disinfection work?

When exposed to the energy emitted by UVc at the right intensity for a given amount of time, the DNA or RNA within viruses, bacteria, and other microorganisms is disrupted, making them non-infectious.

How long does it take for UV to work?

The time it takes UVc to effectively disinfect is a function of the wavelength being used, the lamp intensity, the type of microorganism being targeted, and the distance from the source. With a correctly sized UVc lamp in close proximity to a surface, viruses and other microorganisms can begin to be inactivated immediately.

Does UVa or UVb work faster than UVc?

No. Wavelengths nearest 265nm (within the UVc range) are the most effective for germicidal applications with sharp drop-offs in efficacy at longer or shorter wavelengths.

Is indigo blue light the same as UVc?

No. Indigo blue light has a wavelength around 405 nm which is just beyond the UV spectrum. There are systems that utilize this kind of light for infection control. However, current research does not support this technology’s effectiveness on viruses.

How can I apply UV lighting effectively in my space?

We recommend UVc for two types of sanitization applications: air and surface. The most effective places for locating air sanitization lamps are either within the HVAC equipment itself or installed in the space as an upper room fixture. For surface sanitization, the applications are many and each case needs to be evaluated individually. UVc light will inactivate the virus very effectively when it contacts a surface directly, so flat surfaces like counters, elevator walls, etc. are prime candidates in our opinion. UVc light needs to be directed away from occupants and/or controlled with an occupancy sensor to avoid direct contact with occupants. Additionally, since UVc is still “light,” objects in the beam path will produce shadows, and any surfaces where shadows exist will not be affected by the UVc radiation.

Does UV disinfect surfaces in the “shadows” like the backs of door handles?

Because UVc is still “light,” objects in the beam path will produce shadows, and any surfaces where shadows exist will not be affected by the UVc radiation. However, a caveat to this is dependent upon the reflectance of the surrounding surfaces. We’ve seen research that shows a reduction of bacteria on non-directly illuminated surfaces, but most of that research has been done in a hospital settings, such as in Operating Rooms, which in many cases have a high reflectance on most surfaces including the floor.

Does UV degrade or impact the finishes and materials used within a building?

Just as the sun can degrade certain finishes next to a window, repeated and extended exposure to artificial UV can impact materials within a space. This effect should be considered during design.

Would upper room UV impact the lighting within a space?

Although UV light is theoretically outside the visible spectrum, upper room UV fixtures do emit some visible blue light. How much impact this would have with the visual aesthetic of the space is dependent on the overall illumination level of the upper area of the space.

Do I need to use handheld UV lights on my outdoor surfaces fixtures or does the sun take care of that?

Like mentioned above, the sun’s UVa and UVb wavelengths reach earth, however it’s UVc wavelengths that are the most effective at killing germs. It appears there hasn’t been much research in this area, and that the sun, although a reliable source, doesn’t provide consistent radiation to a surface (due to clouds, rain, etc.). If the surface needs to be reliably disinfected, and time is at a premium, then manual methods (such as handheld UV) would be recommended.

If I install UV, would I still need to increase cleaning protocols?

While UV lighting is an effective tool for sanitation, it has limitations. Complementing this application with other strategies like increased cleaning protocols improves your building’s infection control. Since UV isn’t safe for occupied spaces and doesn’t impact areas outside of the direct light (in shadows), other protocols should be in place. There’s no singular silver bullet, so to speak, but employing multiple tactics augments the effectiveness of each.

Can you just replace the lamps in existing fixtures with UV bulbs?

To accurately answer this question, the existing fixtures’ specifications would need to be known to determine if the UVc lamp could operate optimally. The effectiveness and life of the lamp could be significantly impacted if the ballast isn’t designed to operate with the lamp.

Can UV be easily added to existing AHUs or would the system need to be replaced?

UVc is a straightforward retrofit for most systems. The sizing and exact layout of each system is unique to the configuration of each piece of equipment. So, we recommend seeking the advice of a qualified professional if you’d like to add UV to your existing HVAC.

If I already have HEPA filtration, do I also need UV disinfection? How much extra value does it add?

Like we noted in our Infection Control Technologies for Building Design article, because HEPA filters are typically installed in the ductwork and therefore must rely on the room airflow patterns to carry contaminants to the filter, small particles like viruses can circulate in the room for an extended time before eventually making their way to the filter for capture. In these cases, UV within the space, such as in an upper room configuration, could inactivate these particles before they reach the HVAC system and offer greater infection control. Alternatively, adding UVc within the HVAC system in addition to existing HEPA filtration can inactivate viruses and other microorganisms that may manage to slip through the filter, however, the value that brings is dependent on the facility, its occupants, and the goals of the owner.

What specifications (wavelength, wattage, FDA approval, surface exposure duration, etc.) are recommended for UV?

The necessary specifications depend on the application. However, we would recommend that any specification for a UVc sterilization product should include language around the required reduction and contact time. For example, “UVc lighting manufacturers must recommend sufficient lamp intensity to provide a 99% reduction in active virus count in a 32″ x 40″ duct with air traveling at 700 FPM with 3’ of clear contact length in the duct upstream and downstream of the lamp.”

To discuss the various UV disinfection applications further, contact Dustin or Sean today.