TECHNICAL PRINCIPLES
Ultraviolet radiation and UV-C sources
ULTRAVIOLET RADIATION
Electromagnetic radiation
Visible light
It is located between the wavelengths of 380nm to 780nm. It decomposes in this band of wavelengths, according to the “Colors of the Rainbow” that can be observed after the clearing of sunlight following a good rain storm.
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Non-visible light
On each side of the visible light spectrum is:
– Before red: Infrared (which heats up)
– Beyond violet: Ultraviolet (which destroys).
Ultraviolet rays also known as “UV”
UV (ultraviolet), whose wavelengths are between 100 and 400 nm, are classified into 3 families:
- UVA (315 nm to 380 nm – Long wave)
The main effect of UVA rays is the pigmentation of the skin. They find their application in tanning equipment and, also, for medical treatments, psoriasis. - UVB (280 to 315 nm – Medium wave)
UVB promotes the production of vitamin D and is used for anti-rash applications. These have other uses particularly in adhesive deep curing systems. - UVC (100 to 280 nm – Short wave)
It is between 250 and 270 nm that the germicidal efficiency peak is located . So-called “GERMICIDAL” lamps emit at 253.7 nm radiation at 185 nm is an “ozone creator” from oxygen.
What are these ultraviolet rays applicable to disinfection?
These ultraviolet rays are of the same family as the rays creating our “Visible” light. This “family” is called that of electromagnetic radiations . These rays are classified according to their wavelength, the unit of measurement is the meter or one of its multiples including the nanometer (symbol: nm).
UVC ACTION
LightSources and LightTech Low Pressure Mercury Germicidal Lamps are designed to produce the highest amount of UVC radiation where 90% of the energy is produced at 254nm. This radiation is very close to the top of the germicidal efficiency curve of 265nm, the wavelength most lethal to microorganisms.
ENERGIE AND DOSES
UVC Energy
Each point of a lit UVC lamp emits radiation whose intensity is expressed in µw / cm² and which decreases as a function of the distance from the source. It will therefore be necessary to find the arrangement of the lamps so that the radiation on the element to be treated is optimized and as homogeneous as possible .
ERIES has responded to this need by developing software for calculating the necessary and sufficient UVC energy specifically adapted to each situation.
UVC ENERGY LEVEL NECESSARY FOR THE DESTRUCTION OF 99.9% OF DIFFERENT MICRO-ORGANISMS (mW / cm²)
Opacity
It is important to know that UVC does not pass through fluids and transparent materials like visible light does. When used for the treatment of liquids (and water in particular) calculations must always take into account the coefficient of transmissibility specific to each fluid. For example: “Crystal Vinegar”, totally transparent to visible light, is absolutely opaque to UVC.
UVC dose
For a given microorganism subjected to the action of UVC, the destruction effect depends on the intensity (I) of the radiation it receives and the exposure time (t).
DOSE = I (mW / cm²) xt (s) mJ / cm²
The intensity “I” is characterized by the power of the lamp and its distance from the surface to be treated. The time is linked to the rate of the process or to the flow rate of the fluid in the UVC generator.
The DOSE is a constant characteristic, corresponding to a typical microorganism and it corresponds to the UVC energy necessary for a decrease in its population by a factor of 10 (90%).
The concept of logarithmic reduction corresponds to the percentage of inactivation of the germs present.
- 90% decrease is equivalent to 1 Log
- 99% decrease is equivalent to 2 Log
- 99.9% decrease is equivalent to 3 Log
etc…
To go from 90% to 99% reduction, it will therefore be necessary to double the dose and triple it to arrive at 99.9% (for a specific type of germ).
