Measurement result COBstr Box

In the last couple of months we have seen a tremendous increase in the amount of scientific research into disinfection with UV-C. Two conclusions:

  1. UV-C irradiation can kill bacteria and inactivate viruses, including coronaviruses.
  2. Results and circumstances of the research vary significantly.

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Is 99,99% disinfection with UV/C possible?

Yes, it is possible, but only in ideal circumstances. While designing the COBstr Box we did our utmost to approximate the best possible conditions and we will continue to do so. An example is the system of insertable frames. This allows you to suspend your face mask in a way that the UV-C light can reach as much of the surface as possible (because disinfection does not happen where there is shadow).

Are all UV-C products equally efficient?

Far from it. Many products claim 99,99% disinfection in a few seconds. At COBstr we have done a lot research and we don't believe a word of it.

Measurement COBstr Box

COBstr asked the company Ocean Insight to measure the COBstr Box ( Ocean Insight is market leader in scientific equipment for UV-C devices.

Measurement results

The measurements reveal that the irradiance in the middle of the COBstr Box is over 41 microwatt-second per square centimetre. Zero UV-C was detected outside the Box. The test results are available on request.

What does this mean?

The dose of UV-C that an object obtains can be calculated by multiplying the irradiance, expressed in milliwatt per square centimetre, by the number of seconds that the object is exposed to the UV-C light.

How much radiation is needed to inactivate the corona virus?

Single-stranded RNA viruses, such as SARS-CoV-2, are generally inactivated by exposure of 2-5 millijoule per square centimetre. This applies to hard surfaces. For face masks, made of soft material, the required dose is 300 millijoule per square centimetre. (source: University of Nebraska).

To obtain the 5 millijoule dose that Nebraska University refers to, at 41 microwatt, the disinfection process will take 122 seconds for hard surfaces.
For soft surfaces like face masks it takes 122 minutes to obtain 300 millijoule.

WARNING: disinfection is a relative term. Generally speaking, the dose required for 90% disinfection (“1 log reduction” in medical jargon) is lower than the dose required for 99,9% disinfection (“3 log reduction”), depending on the type of virus. However, high doses can lead to rapid degradation of materials.


The measurement was performed with scientific equipment from Ocean Insight. However, disinfection with the COBstr Box is done at one's own risk and one's own free will. The COBstr Box is available for anybody, from private individuals to SMEs to multinational corporations.

COBstr does not venture to make statements about log reduction. Log stands for “logarithm.” Log reductions tell something about the number of microbes and the viral load. This is important information for medical staff operating in high risk COVID departments of hospitals. The COBstr Box in its current configuration is not intended for disinfecting surgical face masks for hospital staff.

COBstr advises you to remain sceptical about devices claiming 99,99% disinfection in a matter of seconds. This is sometimes based on selective research. Or worse, based on no research at all, without carrying out reliable UV-C measurements, or without considering appropriate safety precautions.