With the rapid growth of UV-C LED applications in sterilization and disinfection applications, there is an increasing need to quantify and determine whether a specific UV-C lamp or device can achieve the purpose of disinfection. Unlike conventional lighting products, we can visually confirm whether it is "bright enough", while UV-C is invisible to the naked eye, which is particularly challenging from a measurement point of view. In this article, we will introduce the main measurement methods and principles, and then work through a few examples that will help complete the steps required to determine the irradiance requirements for a particular setting.
Dosage = amount of UV × time
First of all, we need to start with the UV-C dose, because the ultimate goal is to reach a certain UV-C dose required to inactivate pathogens. But first, what exactly is the dose? How to measure?
UV-C dose (also called exposure dose or fluence) is a method used to measure the total amount of UV-C energy that has been irradiated on a specific surface. This is the most critical element in the design of the UV-C system, because the UV-C dose is the main determinant of whether we successfully achieve pathogen inactivation.
The dose depends not only on the intensity of UV-C falling on the surface, but also on the time that the surface is exposed to UV-C radiation. In other words, if other conditions are the same, a UV-C lamp with an intensity increased by half can be used for twice the time, and the same UV-C dose can be obtained.
The intensity of UV-C falling on the surface is called irradiance, and the unit is W/m² (or some change in power per unit surface area). The exposure time is in seconds.
The simple form of the formula is as follows:
Exposure dose (J /m²) = ultraviolet radiation (W /m²) x time (seconds)
We can also verify this by looking at the unit agreement here (1 Joule = 1 Watt)-second).
What exactly is UV-C irradiance?
The most important part of this equation is the irradiance value. Irradiance is a parameter of energy falling on a specific surface. Irradiance can be affected by three main factors: (1) the intensity of the UV lamp, (2) the distance from the lamp, and (3) the angle relative to the lamp. It may be helpful to consider the behavior of regular light bulbs-for example, a very bright light bulb placed far away from the surface and at an angle to the surface will not provide sufficient lighting on the table surface.
For example,please see the 222nm far excimer lamp below, When the irradiation does reaches at 2mJ, it can start to disinfect. For example, it takes 0.1 minute to reach 2mJ when the targer you want to disinfect is 100 mm away from the lamp. The higher the irradiation does, the higher the disinfection rate.