With the COVID-19 pandemic of 2020 in full spate, many concerned people are turning to ultraviolet (UV) light sources to destroy the virus and other dangerous pathogens. Notably, the ultraviolet-C (UVC) portion of the electromagnetic spectrum has become a highly coveted means of disinfecting large areas and even indoor air. This type of disinfecting light is regarded as ultraviolet germicidal irradiation (UVGI).
Naturally, I had to try out one of the UVGI light sources for myself, but not without some well-deserved scrutiny. Agencies, including the United States Federal Trade Commission (FTC) have been warning consumers for years to watch out for falsely-advertised UVGI products. Unfortunately, online marketplaces are dealing with both types of plagues—as ineffective and difficult-to-test fake UVGI products permeate the market.
With that in mind, the objective here was to test a UVGI light I had purchased in March 2020.
Safety Precaution
Before getting started, note the ultraviolet light spectrum is hazardous in large or uncontrolled doses. When in doubt, assume there is no safe level of personal exposure to the UV light sources featured here. Keep their light emissions away from plants, pets, and people.
Some UVC products will also generate ozone (O3) gas while operating. Ozone is chemically aggressive and can cause respiratory problems.
Germicidal Lamp Operation
By May of 2020, the development of new UVGI tools was accelerated by two problems: the severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) virus, and the resulting disease it causes: COVID-19. The SARS-CoV-2 virion itself is a particle that can be destroyed by the light that the LED lamp’s seller claims it emits…
Most of the light we humans can view falls in the range of 400 nm (violet) to 700 nm (red) (1 nm = 1 nanometer, or 1×10-9 meters). The invisible, ultra-violet range of light is split into 3 subgroups that are relevant to this test:
- UVA: 315 nm to 399 nm
- UVB: 280 nm to 314 nm
- UVC: 100 nm to 279 nm
The UVC portion is the most relevant one here. Photons in this range of the electromagnetic spectrum are energetic enough to break molecular bonds, making them hazardous to viruses and living organisms.
Artificial UVC light sources of the 19th, 20th, and 21st centuries came in many forms. The two that are most relevant to this test are the low-pressure mercury vapor lamp, and the ultraviolet light-emitting diode (UV-LED).
Mercury vapor light sources emit the two resonance lines of the mercury atom (253.7 nm and 185.0 nm). The wavelength of 254 nm is effective at reducing the infectivity of viruses like influenza A (H1N1) and other coronaviruses. Moreover, the broader range of about 100 nm to 320 nm can also be generalized as germicidal.
The shorter mercury emission of 185 nm will dissociate environmental oxygen molecules (O2) into lone oxygen atoms (O + O). These lone oxygen atoms can each combine with 2 additional oxygen molecules to produce ozone (O3).
Both wavelengths result in germicidal chemical processes. Their objective is to deliver a large enough dose to either destroy germs outright, or damage them beyond replication. The presence of elemental mercury in these lights is a health hazard, so a newer technology based on UV-LEDs is gaining traction with consumers.
The UVC dose is measured in “energy/surface area” units such as millijoules per square centimeter (mJ / cm2). In a similar fashion, the dose required to disinfect against a specific pathogen follows the same logic. Technical literature may use the inverse: “surface area/energy” to describe a germ’s susceptibility to UVGI.
Unboxing the LED Lamp
The lamp was advertised as having an irradiation area up to 500 ft2 (46.5 m2). This implies an effective radius of about 12.6 ft (3.84 m). However, the UV intensity (W/cm2) observable from any given distance was not specified. With all that in mind, it was time to open the box and have a look.
Immediately noticeable was the absence of any kind of a logo, trade name, or identifying branding. This was not particularly encouraging, but the rest of that commentary will be saved for later.
The entire lamp consists of 8 arrays of 22 discrete LEDs, plus a circular formation of LEDs on the top. White-emitting lights similar to this also feature yellow-tinted LEDs, which get their color from the phosphor: cerium (III)-doped yttrium aluminum garnet (Ce:YAG or YAG:Ce3+). This lamp is not white-emitting, and the LED lens material was a duller yellowish white. There was another color visible under direct sunlight. Again, more on this later.
The base of the bulb is the Edison Screw (ES) type E26/E27. This base is common in North America’s residential light fixtures and will fit them without adaptation. If the product’s listing is to be trusted, it is also compatible with the 110-volt mains voltage common in the American home.
Testing the Lamp
Because the requisite UVC band is invisible to humans, only a dosimeter or a specialized light-measuring instrument can indicate whether the device works as advertised.
The dosimeter card shown above in Figure 6 features photo-chromatic ink that is engineered to change color under 253.7 nm exposure. An unexposed dosimeter will feature a large yellow circle at its center.
The center circle will then transition to orange after receiving a dose of 50 mJ/cm2. It will turn purple/magenta with a dose of 100 mJ/cm2.
With that in mind, the dosimeter card was placed within 3 cm of the LED lamp. This card was paired with the reference card in Figure 8 below. The reference dosimeter always accompanied the dosimeter under test, but it was never exposed to the LED lamp. This measure was taken in case environmental factors such as indoor lighting had undocumented effects on the dosimeter.
Next, the room was completely darkened for testing.
30-Second Exposure
First, the lamp delivered an uninterrupted 30-second exposure.
5 Minute Exposure
Next was a 5-minute exposure test using a fresh dosimeter card.
Again there was no apparent response from the dosimeter.
1-Hour Exposure
Finally, a third dosimeter was irradiated for 1 hour.
After an hour’s time, the response from the dosimeter card was barely noticeable. The center area had slightly shifted toward orange. This change would probably not be noticeable without having the unexposed reference around for visual comparison. And it fell short of the distinct orange reference color printed on them.
Testing an Alternate Light Source
At this point, it’s reasonable to wonder “are the dosimeters working?”
To address this, a different type of UVC lamp was added to the test. The low-pressure mercury arc bulb featured below operates off a low-voltage DC power supply of about 10 V to 16 V. The bulb’s rated power was only 3 watts. Operationally, the low voltage made the bulb easy to work with. But it still requires a current-limiting ballast for proper function.
Like before, the dosimeter was repositioned to be 3 cm away from the bulb.
After 30 seconds of exposure…
As the image indicates, the 30-second exposure with 3 cm separation delivered close to 100 mJ/cm2.
Analysis and Perspectives
With the testing complete, it was worth revisiting the fact that the LEDs did not have a transparent quartz window. Unlike plastics and common sodium-lime glass, quartz is transparent to UVC radiation. Proven UVC LEDs such as the SML-LX3636V or even the now-obsolete VLMU35CM00-280-120 feature a clear quartz lens for this reason.
Instead, the LEDs of this lamp were made of a translucent material, like the diffused lens common in white LEDs that contain YAG:Ce3+.
The discrete LEDs on the lamp also seemed to give off a greenish cast under natural sunlight and fluorescent lamps. This led me to check whether the LEDs would fluoresce under a non-germicidal UVA light source (with a peak near 390 nm to 400 nm).
Sure enough, even with no electric power applied, the discrete LEDs fluoresced bright green under UVA excitation. If nothing else, this is unlike any other UVC device mentioned here so far.
Conclusions
The exact wavelength of “254 nm” was specified by the LED lamp’s product description. Given the failure of the LED lamp to color-shift any of the 3 dosimeter cards as expected, this lamp is not at all likely to be a significant source of the germicidal 254 nm photon. If it is somehow a source, then the intensity is insignificant compared to the low-pressure mercury arc lamp.
However, this test was also limited. The dosimeter card itself is engineered to respond to the 254 nm mercury line. Therefore, the test did not rule out the possibility of other ultraviolet light emissions coming from the LED lamp. This includes ultraviolet emissions that might still be germicidal or harmful to humans.
For a more comprehensive test, a radiometer or a similar light-measuring instrument should be used to measure the lamp’s emissions across the entire germicidal range.
For now, I will be avoiding this LED-based product: both as a disinfection tool and as a general light source.
References
| [1] | U.S. Federal Trade Comission, “FTC: Lights Out for Falsely Advertised UV Disinfectant Devices,” U.S. Federal Trade Comission, 20 Aug. 2015. [Online]. Available: https://www.ftc.gov/news-events/press-releases/2015/08/ftc-lights-out-falsely-advertised-uv-disinfectant-devices. [Accessed 15 May 2020]. |
| [2] | UL LLC, “Assessing the Photobiological Safety of LEDs,” 2012. [Online]. Available: https://legacy-uploads.ul.com/wp-content/uploads/sites/40/2015/02/UL_WP_Final_Assessing-the-Photobiological-Safety-of-LEDs_v3_HR.pdf. [Accessed 16 May 2020]. |
| [3] | P. Flesch, “Light and Light Sources,” in Light and Light Sources – High Intensity Discharge Lamps, Berlin, Springer, 2006, pp. 1-50. |
| [4] | J. J. McDevitt, S. N. Rudnick and L. J. Radonovich, “Aerosol Susceptibility of Influenza Virus to UV-C Light,” Applied and Environmental Microbiology, vol. 78, no. 6, pp. 1666 – 1669, 2012. |
| [5] | C. M. Walker and K. Gwangpyo, “Effect of ultraviolet germicidal irradiation on viral aerosols,” Environmental Science & Technology, vol. 41, no. 15, p. 5454, 2007. |
| [6] | M. Eickmann, U. Gravemann, W. Handke and et. al., “Inactivation of three emerging viruses – severe acute respiratory syndrome coronavirus, Crimean-Congo haemorrhagic fever virus and Nipah virus – in platelet concentrates by ultraviolet C light and in plasma by methylene blue plus visible light,” International Society of Blood Transfusion, pp. 146-151, 2020. |
| [7] | W. Kowalski, “UVGI lamps and fixtures,” in Ultraviolet Germicidal Irradiation Handbook, Berlin, Heidelberg, Springer, 2009, pp. 119-137. |
| [8] | “UVC exposure (254 nm) of UV sensitive material at different irradiation levels,” 8 Nov. 2017. [Online]. Available: https://www.americanultraviolet.com/germicidal-healthcare-solutions/documents/RISE-Report-UVC-exposure-Intellego.pdf. [Accessed 16 May 2020]. |
| [9] | Ushio America, Inc., “Germicidal Low Pressure Mercury Arc,” 2020. [Online]. Available: https://www.ushio.com/files/specifications/germicidal-low-pressure-mercury-arc.pdf. [Accessed 16 May 2020]. |
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