WHAT IS UV-C LIGHT?
This invisible radiation includes the wavelength range of 100 nm to 400 nm. UV light can be further subdivided and categorized into separate regions:
Far UV or vacuum UV
(these wavelengths only propagate in a vacuum)
200 nm to 280 nm
UV-C - useful for disinfection and sensing
280 nm to 315 nm
UV-B - useful for curing, tanning and medical applications
315 nm to 400 nm
UV-A (or ”near UV”) - useful for printing, curing, lithography, sensing and medical applications
THE PHYSICS OF UV-C LIGHT - SHADOW
By far, the most powerful source of UV-C radiation in the solar system is the Sun. The amount of UV-C generated by the Sun every second is higher than all of the artificially generated UV-C in the history of UV-C disinfection combined (see Fig. 2).
Imagine being on holiday in Spain mid August and the dangers of spending too much time in the Sun. Sunburn is a well-known result of overexposure to UV light. Now, have you ever stopped to think why you cannot get a sunburn at night? The answer is simple! The part of The Earth facing the sun blocks the light from the part facing away from the Sun. Otherwise known as day and night (see Fig. 2).
If we now apply this fundamental law of physics to a patient room or operating theatre scenario, how can we expect a man-made device to accomplish what the Sun cannot? The only effective approach to avoid shadowing in a healthcare setting is to reposition the light source (UV-C device) as many times as necessary.
THE PHYSICS OF UV-C LIGHT - INTENSITY OVER DISTANCE
THE INVERSE SQUARE LAW
Just like shadow, another law of light that complicates the use of UV-C as a room disinfectant is intensity over distance. The loss of light intensity over distance can be easily calculated using the inverse square law.
We know that UV-C intensity at 1m is 100% therefore, the light intensity at 2m will fall to 25% (a quarter). At 3m the intensity drops further to 11% (a ninth) and at 4m, the intensity is only 6.25%.
The inverse square law dictates that when we want to reach the same level of UV-C intensity (or germicidal effect) achieved at 1m distance, it is necessary to radiate for 9 times longer from 3m distance and 16 times longer from 4m distance.
THE PHYSICS OF UV-C LIGHT - REFLECTION
UV-C has a very short wavelength which means approximately 95% of the energy is ab- sorbed by many types of molecules present in modern plastics and paints. Only 5% of the UV-C energy can be utilized for disinfecting objects in shadow from direct UV-C rays.
In a realistic healthcare environment reflection is often combined with distance as the examples 1 and 2 illustrate. In order to radiate UV-C on to the blind side of a hospital bed rail, the light must first travel to the wall in order to be reflected. This means that the 95% loss of energy due to reflection is not the only loss of energy to consider. Addi- tionally, the loss of intensity as per the inverse square law must be calculated:
EXAMPLE
Calculation of UV-C radiated onto the blind side of hospital bed rail (marked in red).
Distance light travels is approx. 4 metres = UV-C light intensity is approx. 6.25% (a sixteenth). Energy reflected off the wall = 5% (95% absorbed).
Total UV-C radiated onto blind side of hospital bed rail = 5% of 6.25% = 0.3% Conclusion with example 1:
1 minute direct UV-C at 1 metre = 300 minutes of reflected UV-C
How Does Krypton Far UV (222 nm) Work?
Superior Option
Safety
Effective for Sanitizing
The 222nm Far UV Difference
Credit: Dr. David Sliney, Johns Hopkins School of Public Health
Far UV (222 nm) Krypton Applications
- Defense and Government facilities
- K-12 schools and universities
- Healthcare facilities
- Transportation (buses, airplanes, trains, subways, ferries and cruise ships)
- Public facilities (airports, city halls, courts, museums, theaters, amusement parks, bathrooms)
- Detention centers
- Elderly care facilities
- Childcare facilities
- Commercial office, elevators, and stairwells
- Hotels, resorts, and casinos
- Restaurants/Retail
- Athletic facilities (stadiums, locker rooms, suites and equipment)
- Houses of Worship
- Entertainment Venues
- Conference Centers
- Food preparation, delivery and shelf life applications
- Grocery and convenience stores
- Industrial facilities
- Space applications