Authored by: Ye Zhang, PE; Joyce Kelly, R.A.,* GLHN Architects & Engineers, Inc.

Germicidal UV light irradiation, used for over 100 years, is currently available in half a dozen flavors to deactivate viruses and bacteria in air, water, and surfaces. The RNA of SARS viruses related to Covid-19 virus breaks down with sufficient light in the UV-C spectrum, at the right distance with enough time. Labs evaluate these variables to determine the intensity of the UV-C light source, distance from the target and the optimum length of exposure time. UV-C treatment is now vital to healthcare facilities as well as transit applications, schools and universities, and businesses including offices, hospitality, assisted living, and sports facilities.

Between sterilizing equipment in biosafety cabinets and disinfecting empty rooms and buses with robots, the use of UV-C lamps is accelerating exponentially. The same light source has been used for disinfecting water extensively since 1998, and is highly regulated by the FDA due to the damaging effects of UV-C. To mitigate these effects UV-C fixtures aimed above 7’ can safely treat upper room air avoiding human exposure in occupied rooms. Temporary hospitals in resource-challenged countries are installing UV-C fixtures with built-in vacancy sensors to avoid exposure. Less reliably, humans garbed in protective gear to protect their skin and eyes wield UV-C wands to disinfect surfaces for mobile and temporary solutions. Photonics World Covid-19 update: 25 June 2020


Airborne pathogens are the toughest to deactivate because they float and move. Factors include humidity (40-50% recommended), velocity and the fraction of fresh outside air. Progressive utilities like Salt River Project[1] (SRP) and Tennessee Valley Authority (TVA) are offering an incentive of $30 per ton toward the purchase and installation of ultraviolet germicidal irradiation in commercial HVAC systems.[2] When UV-C lamps are positioned next to the cooling coils where return air velocity slows down, 95% disinfection rates of recycled air can be achieved with careful design. However, high velocities and cold temperatures reduce UV-C’s effectiveness. Fewer UV-C lamps are needed to deactivate upper room air than cooled, recirculated air in supply air ducts.

The sweet spot for traditional UV-C is a wavelength of 265nm. UV-C is still a mercury or xenon based light source at this point and the warmup period for these lamps is 1-5 minutes before full effect is achieved.[3] Expect to swap out lamps yearly because they have a 10,000-hr. life expectancy. Induction-type mercury sources last longer and are recommended if you can find them. LEDs currently have about 3% of the intensity in the UV-C wavelength. This will change rapidly because they can be manufactured with specific materials that produce peak output at UV-C wavelengths. Moreover, LEDs thrive in cold environments.

Far-UV-C, excimer lamps, with a shorter wavelength of 222nm, work more slowly but carry less risk to penetrate live DNA under mammalian skin or eyes, pending studies on humans. In June 2020, Columbia University reported that Far-UV-C light safely kills airborne coronaviruses. The Illuminating Engineering Society (IES) reports that Far-UV-C may pose a hazard to the cornea and significant skin hazard. Based on their results, the researchers estimate that continuous exposure to Far-UV-C light at the current regulatory limit would kill 99.9% of airborne viruses in about 25 minutes.[4] If safety for human health exposure is substantiated, Far-UV-C could expand applications in occupied spaces.

Controlled timing of length of exposure is key. Timing is a function of intensity and distance, as well as scheduling[5]. The simplest method is to incorporate a vacancy sensor that prevents the light from activating when warm bodies move within its range. Long distance remote control works with a wired system or 50’ max. depending on barriers, for a wireless remote.

As spot solutions, you may notice UV-C fixtures in hospital corridors and waiting rooms, aimed toward the ceiling. In 2019, the CDC indicated that “…ceiling fans with upward airflow rotation combined with upper-air ultraviolet germicidal irradiation (UVGI) disinfection systems can be utilized.” [6] UV-C fixtures are also used increasingly in commercial kitchens and dining facilities.

New light sources and spectrums, safer exposure controls and testing are refining UVGI rapidly. Used carefully, it’s a promising tool to deactivate pathogens like the Covid-19 virus. Incorporating UV-C treatment into a whole building solution can balance health with energy efficiency. The following case study describes a layered plan of UVGI strategies.


This summer, GLHN Architects & Engineers received a theoretical question about UV-C disinfection treatment applications for a sizeable renovation. After rapidly updating our expertise, the following economical solution was offered.

Upper-air UV-C light fixtures, wall-mounted 7’ above the floor, would be aimed up into a 10’ high space. They would only activate after two measures of occupancy are deployed: a CO2 sensor indicating spaces have recently been occupied and vacancy sensors indicate people are no longer present. This way energy isn’t wasted treating spaces that aren’t being used and people won’t be exposed to UV light.

UV-C lamps with an average of 254nm and minimum intensity of 10uW/cm² could be positioned to achieve at least 100 feet of coverage per minute with wall-mounted fixtures. Spraying titanium dioxide on surfaces would enhance dispersion of light waves. Additionally, UV-C light may be added near the cooling coils to purify the return air. For the most vulnerable populations, this two-fold approach would be ideal, but upper air UV-C treatment alone is the most affordable.

Further refinements include customizing the unit for manual programming and calibration or integrating it with the facility Building Automation Software (BAS). Then the building management team could program and monitor the operation of these lamps through the BAS system dashboard of their existing Delta System.

The redundant safety systems ensure the unit will not activate while the room is occupied and will immediately suspend operations if motion is detected in a previously unoccupied room. If interrupted, the unit will resume its programmed cleaning cycle after motion is no longer detected.

System Costs

The cost of these systems varies widely depending on approach, scale and controls required for a complete system. Modern technologies, such as LEDs, will increase prices as they decrease energy use and maintenance costs. For a simple space layout, a design including UV-C fixtures may double the cost of merely illuminating the room.

Health Hazards of UV-C

  • UV-C deactivates bacteria and viruses, by damaging DNA/RNA and can damage ours.
  • Can cause sunburn and temporary inflammation of the cornea (Photokeratitis), skin cancer and ocular cataracts.
  • Requires use of PPE: UV absorbing full-face shields, gloves (nitrile, latex, or tightly woven fabric); and lab coat that allows no skin to be exposed to decrease exposure risk.
  • Most UV-C sources are currently mercury-based and should be disposed of with care.
  • NIOSH (National Institute for Occupational Safety and Health) recommends the time of exposure to an intensity of 100 mW/cm² at wavelength 254 nm not to exceed 1 minute. However, no exposure level is completely safe.
  • Upper room air treatment may be safe when fixtures are mounted above 7’ with shielding and optics preventing direct exposure. Recommend using Far-UV-C (222nm) excimer lamps for maximum safety.
  • The balance of performance/safety is not yet definitive, pending current and future studies.

 Checklist of key information to look for in manufacturer’s specification sheet and/or literature:

☐  Wavelength:

  • UVC: 200-280 nm (265 nm)
  • Far-UVC: 207-222 nm (222 nm)

☐  Supply Voltage requirements

☐  Power Consumption (12-24V, 120V)

☐  Operation Life

  • Low pressure Mercury GUV – 10,000 hours
  • UVC LED – 100,000 hours (still in development)

☐  Control option: Building Automation System, Vacancy sensor, Time switch, Manual

☐   Power connection: hard-wired, plug in

☐   Lamp Configuration: Linear, Bulb, LED

☐   Mounting type: Wall (straight or corner), Suspended

☐   UVC radiation efficiency: (LED’s current low efficiency will change!)

☐   Lumen depreciation:

☐   Warm-up time: (May range from 0 – 5 mins. depending on lamp type)

☐   UVC output related to ambient temperature:

☐   Ambient temperature limits: (Standard quartz will overheat at 40°C.)

Mercury content:

Any (tiny) Footnote/Remark/Disclaimer that may limit or negate design effectiveness

☐    Material Safety Data Sheet (MSDS), manufacturer’s safety cautions, use restrictions, user manual and recommended PPE (if applicable)

 Testing, Regulations and Standards


☐    ANSI/IESNA RP-27: Photobiological Safety and Risk or IEC 62471: Photobiological Safety or Lamps and Lamp Systems[7]

☐    UL 1598: Luminaires

☐    UL61010-1: Standard for Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use – Part 1: General Requirements

☐    IEC 61347: Lamp Control gear

☐    IEC 62031: LED Modules for General Lighting – Safety Specifications


☐    UL 979, C22.2 No. 68-09: Standard for Water Treatment Appliances

☐    IEC 60529: IP68

☐    IEC 60068: Environment Testing

☐    FDA Regulations

[1]Salt River Project.

[2] Tennessee Valley Authority.



[5] Exposure Example: UV-C dose of 5 mJ/cm2 with exposure time 6 seconds resulted in 99% reduction of SARS-CoV-2 virus on surface. UV-C dose of 22mJ/cm2 with exposure time 25 seconds results in reduction of 99.9999% of SARS-CoV-2 virus on surface. (National Emerging Infectious Diseases Laboratories (NEIDL) Boston University.


[7] UL: UVC germicidal products reference guide.

*Thank you for your contribution: Brandon Wilson, Electrical Designer,; Lisa Vickery, Electrical Designer; Mensah Folly, Electrical Designer II,   Authors:  Ye Zhang, PE, Electrical Engineer,; Joyce Kelly, R.A., CxA+BE, LEED AP BD+C, Architect / Commissioning + Green Building Specialist,

GLHN AE, Inc. is an employee-owned firm headquartered in Tucson, Az with an expanding office in Phoenix. The firm offers integrated, multi-discipline services in architecture, civil, mechanical, and electrical engineering. GLHN’s staff includes LEED Accredited Professionals in all disciplines (LEED AP); Green Globes Professionals (GGP); Building Energy Simulation Analysts (BESA); Certified Energy Managers (CEM); Energy Reduction Analysts; Certified Commissioning Providers and Technicians (Cx and CxT); staff Certified in Plumbing Engineering (CIPE); and a Lighting Certified (LC) designer.

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