Far UV lamps using band pass optical filters rendered essentially useless because of the filter and diffusers.

Far UV 222nm lamps produced by all other manufacturers need to use band pass optical filtering due to their extreme secondary and tertiary emissions at wavelengths that are harmful for human exposure.  This is necessary because they do not understand the 21 factors that control a 222nm lamp, some of which minimize those harmful emissions.  As a result of having to use the optical filter, the effective output of the lamps are reduced by as much as 60%.  Coupled with the use of a diffuser to increase the output field of the lamp from 40º to 80º, the effective output of the lamps are reduced by a total of 80%.

Given that these other lamps are woefully underpowered to begin with (input power from 3W – 15W), the efficacy of these lamps is called into question.  When compared to a 150W Sterilray lamp, the underpowered competitor lamps would require anywhere from 20  to 50 lamps (or more) to match the total fluence output from a single Sterilray lamp.

An unbiased review of the 2015 “Woods Study”

The 2015 “Woods Study” is often cited by our Far UV manufacturing competitors who claim you need a filter on the Sterilray Far UV lamps to protect against the emission of wavelengths potentially harmful to humans.

While it is known that Far UV lamps used by Ushio, Far UV technologies, R-Zero, UV Medico, Puro, Beacon, and others all have band pass optical filters, the reason is simple.  The lamps would not be usable as safe for humans without the filter.

What do we know about the “Woods Study”:

  • Funded and in part, authored by GOJO, parent company of Purell.
  • Sample size of only two skin types with N=1 each!
  • Study conclusions are not supported by the data.
  • Many anecdotal references without citations.
  • Spectral analysis used in the study shows extremely little secondary emissions from the Sterilray lamp.

Why do Sterilray lamps not need a filter?

The issue surrounding optical filtering really boils down to the fact that not all excimer lamps are created equal.  Over the 25 years that we have been making excimer lamps we have perfected the technique through the identification of 21 different factors that control lamp performance.  Such things as lamp life, lamp efficiency, ozone production, and spectral output are affected by the gas mixtures, the level of atmospheric pressure, and the use of a phased pulse power supply.  These are just a few of the controls that enter the equation.  The use of optical filtering was necessary for Ushio and other excimer lamp producers because their lamp performance was such that they output secondary and tertiary emissions in such high output that their lamps were simply not safe for human exposure at the established ACGIH TLV levels for those additional wavelengths.  In other words, they created a marketing story that all excimer lamps need filters, when in fact that is not the case.  Others that manufacture Far-UV lamps are woefully underpowered, and their performance comes nowhere near the performance of the Sterilray lamps.  The other Far-UV lamp manufactures simply don’t understand the 21 factors that produce a high performing 222nm excimer lamp.

Furthermore, Far-UV Sterilray™ lamps are manufactured in such a way that a secondary output at 257nm is less than 1/90th the output at 222nm.  The current TLV for the 222nm wavelength is approximately 479 mj/cm2 for skin exposure.  That is a time weighted value for eight hours of exposure in a five-day work week.  The time weighted TLV for 4 hours of exposure is double or 958 mj/cm2.  If we were to configure our lamps to hit the 479mj/cm2 TLV, our secondary output at 257nm would be at 479/90 or 5.3 mj/cm2, well below the existing TLV for 257nm, which is 10 mj/cm2. Even if Sterilray lamps were powered to the 222nm TLV limit (which they don’t even get close), Sterilray lamps would still be considered safe because of the low emissions at those other wavelengths.  The competitors don’t understand the basics of the ACGIH TLV exposure limits and simply don’t understand how to properly configure a space to provide for adequate viral protection.

Spectral analysis GermBuster Sabre

Study funded by 3M Corporation

Spectral analysis of the 500w GermBuster Luminaire

Study funded by Healthe, Inc.

Spectratox Woods spectrgraph

Spectratox (aka Woods Study) funded by GOJO

Contact us 


603-516-2050                  marketing@sterilray.com