In the age of COVID-19, more and more people are turning to UV-C light as a means to disinfect everything from surfaces to surgical instruments. As we've highlighted in other blogs, UV-C light provides a great method of disinfection against infectious diseases and viruses, without the drawbacks and after effects that accompany chemical disinfectants and fogs.

When using UV-C light for disinfection, it's important that the proper amount - or dose - of light is applied in order to effectively irradiate the target.  Every microbe has a calculated dose for deactivation.  This calculated dose is seen as a formula where dose is the product of irradiance and exposure time.

Verifying the actual amount of light reaching a surface is a critical step in the disinfection process, as many factors can impact this.  In order to get an accurate measurement, a light meter that will integrate multiple measurements over the exposure time must be used. 

The below graphic offers an easy-to-understand visual on why measuring dose, and not just calculating it, is important. 

WHAT IS DOSE?

● Dose (or exposure) is the sum of how much light a surface has received during a given time period expressed in the units of J/cm2.  ● J/cm2 is often shown with a prefix (m or µ) to indicate the number of decimal places.  ● For example: 0.002 J/cm2 could also be written as 2mJ/cm2.

THE FORMULA

● Dose is often measured directly on a light meter that has the ability to integrate (sum up) the total, but Dose can also be calculated. ● Formula for dose: Irradiance * time (seconds) ● Formula may be expressed as mW/cm2 *sec= mJ/cm2 ● ie: 5 mW/cm2 with a 10 second exposure time generates 50 mJ/cm2

USING AVERAGE IRRADIANCE FOR DOSE

● Since many UV sources are not stable a more accurate dose can be achieved using the formula: Average lrradiance *seconds= J/cm2 ● Example: During 10 second exposure time, the light level changes from 5 mW/cm2 to 4.2 mW/cm2 ● 3 irradiance measurements of 5, 4.2 & 4.2 mW/cm2 generate an average irradiance of 4.467 and a calculated dose of ( 4.467 x 10 sec=) 44.67 mJ / cm2

WHY IT MATTERS

Inaccurate dose measurement can lead to: ● Under exposure (germs are still able to spread) or Over exposure (shortening of lamp life & increased risk of UV degradation) ● During disinfection, lamp warm up is not always possible or ideal so using 1 irradiance measurement (i.e: 50 mW/cm2) can provide an incorrect value, and averaging can be time consuming and be less accurate ( 44.67) where as our IL T2400 meter can provide accurate dose for both Long and short integration times. (43.6)

ILT UVGI light meters have the ability to measure, graph and record the dose during the UV disinfection processes.  Our meters can be configured with sensors for UVC covering a range of 185 to 280nm as well as broadband UV sensors covering UV, and VIS. ILT light meters can measure at speeds of up to 20 uSec for pulsed light sources as well as for accurately tracking changes intensity over time to assure accurate dose measurements.

ILT2400 Meter showing dose measurement in Trend Mode