Recently, Signify and Boston University partnered to test whether Signify's Philips TUV UVC light bulbs could inactivate the virus that causes COVID-19. The result of the research showed that ultraviolet-C light at sufficient doses can inactivate the SARS-CoV-2 virus.
Why It Matters
For several months, businesses, governments, and consumers have been buying ultraviolet air and surface disinfection systems with the potential that it would be effective against the COVID-19 virus. This research by Boston University and Signify is the first, clearest proof that the virus is susceptible to UVC germicidal irradiation.
By the Numbers
With this research, users of UVC lights for disinfection can ensure they are reaching thresholds of ultraviolet dose that is applicable to their environment.
- 5mJ/cm2: At this dose of UVC light, a reduction rate of 99% was achieved. With the light that the researchers used, this was about 6 seconds of irradiation time.
- 22mJ/cm2: The researchers estimated that this dose of UVC light would achieve 99.9999% reduction of the SARS-CoV-2 virus. Under the conditions used in the study, this level was estimated to be reached in 25 seconds.
The research was done in a university lab under favorable conditions for testing. Under real world conditions, UVC dosages higher than that indicated by the research may be required to inactivate SARS-CoV-2 or other microbes. A wide range of environmental factors can play a role in reducing ultraviolet light efficacy.
How to Measure UVC Dose
- 6mJ/cm2: The 6mJ dosimeters were originally designed as personal exposure indicators. However, they can also work as "quick check" dosimeters to indicate when UVC irradiation has reached the 99% SARS-CoV-2 reduction level suggested by the Boston University/Signify research.
- 25-50-100mJ/cm2: For medical situations, dosimeters that measure up to 25mJ should be the standard. The tri-color dosimeters that indicate 25, 50, and 100mJ are the best fit.
- 500-1000mJ/cm2: For other applications, including disinfection of N95 masks up to the CDC recommended level, the 500/1,000mJ dosimeters can be used. This is a very large dose of UVC light, so will take much longer than the other dosimeters to reach the final color change.
For an electronic reading of UVC wavelengths at various distances, a UVC light meter can also be used. These are at a higher price point than dosimeters, but well worth the investment for building managers, OEM equipment manufacturers, and medical institutions that need measurements at various times and distances.
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