How do you check the presence of UV-C light

UV-C light has been used for many years in surface, water and air disinfection.. Research has shown that, with the right distance, time and value of radiation, it can be very effective against the spread of micro-organisms. However, the radiation emitted by UV-C light is not visible to the naked eye. So how can we tell if a source of light actually works?

Measuring UV-C Light

Since UV-C light is not perceptible on its own, manufacturers often add colour to UV-C radiation (e.g. by means of LEDs), thus allowing people to see whether a UV-C lamp is on. This is done, among other things, to prevent users from being exposed to harmful UV-C light. But LEDs are not the only way to show whether a UV-C lamp is on. The presence and effectiveness of UV-C radiation can also be measured in other ways, namely with light meters.

It is important that the UV-C light reach the entire surface of the area to be disinfected. It is also very important for hospitals, care institutions and laboratories that the correct disinfection values be attained, to ensure the safety of their staff and patients. If a UV-C disinfectant does not attain the correct values, major problems may ensue. Both the reach and the values of a UV-C device can be measured with light meters. In this article we will explain which UV-C light meters can be used to detect the presence of UV-C radiation in disinfection devices.

How to measure UV-C light with a radiometer

UV-C light cannot be seen with the naked eye. Special meters, such as radiometers, allow one to measure invisible UV-C light. Radiometers are devices that measure thermal radiation and thus also UV-C light. The main components of the radiometer (figure 1) are the UV-C sensor and the display. A UV-C sensor consists of a receiver which detects the properties of UV-C and then converts this into a numerical value. This value is shown on the display. The numerical value can be the UV-C irradiation or dose. There are two different types of units which express UV-C radiation levels.

  • irradiation, in watts per area (W/m2): UV-C radiation is present if the power of the radiation can be measured. This power is often described as irradiation and can be used to calculate the UV-C dose.
  • Dose per surface area (Joule/m2): The UV-C dose is the total amount of UV-C absorbed by a surface area in a given time. The higher the measured dose, the more effective the UV-C radiation is and thus the more active the disinfection process is.

  It is important that the correct value be measured. The effectiveness of UV-C light depends on the combination of exposure time, radiation level and distance. This combination ensures that the correct log reduction is achieved – which is to say, how thoroughly a decontamination process reduces the concentration of a contaminant. In order to achieve a reduction of various bacteria or viruses, a specified minimum dose of UV-C light must be administered during the disinfection process. Read more about this in ‘What Is Log Reduction and What Is It Used for?’.

In order to take the correct measurement, the sensors must be placed near the UV-C lamps, which will result in precise measurement results.

It is important, however, that the correct settings be entered in the radiometer. A UV-C radiometer intended to measure UV-C at a wavelength of 254 nm (UV-C light) will not be able to properly detect the light from other UV-C sources such as UV-C LED, far-UVC or pulsed-xenon UV-C. Sources such as UV-C LED lighting have a wavelength that is not 254 nm. Therefore, it is vital that the right equipment or settings be selected.

How to measure UV-C light with a dose indicator (dosimeter)

UV-C dose indicators are used to check whether the correct UV-C dose can be achieved. Dose indicators (also referred to as ‘dosimeters’) are stickers of sorts. They allow you to see whether UV-C light reaches where you want it to reach, and thus to check whether the entire product or surface will be disinfected correctly. If you have any concerns about whether a particular area will be reached, for example due to shadows (read this article), you can use these stickers to test. If the disinfection cycle is activated, the material on the dose indicator will be exposed to UV-C radiation.

Depending on the amount of energy to which the indicator is exposed, the colour of the sticker will change. The colour of the sticker can then be analysed. For example, with some brands, if a sticker turns yellow, it means that no UV-C light was measured, whereas a red sticker means that UV-C light was measured! In other words, the colour of the sticker will change if the sticker has been ‘touched’ by UV-C. This is an easy and quick way to check whether UV-C light is reaching all the required places.

A disadvantage of dosimeters is that the stickers may change colour because of exposure to other sources of light, e.g. regular sunlight, even when they are not being directly exposed to UV-C. UV-C dosimeters should therefore be stored in a dark place when not in use.

Choosing the right UV-C light meter

Now you may be wondering which type of UV-C light meter to choose. A major advantage of radiometers is that they provide precise qualitative measurement results. They measure both irradiation and dose. The measurement results can then be used in a graph for research purposes. UV Smart recommends the use of UV-C radiometers if you wish to conduct research on the power and effectiveness of UV-C radiation.

Dosimeters, on the other hand, can be used for quantitative measurements. They only allow you to check whether a UV-C dose was actually measured. This is extremely useful if, for example, you are using a UV-C robot to disinfect an area, in that you can see at once where the robot can and cannot reach. Even if there are holes in the object to be disinfected, you can check whether the UV-C light reaches these holes. Dosimeters are generally accurate and very easy to read. This is why UV Smart recommends using dosimeters when you want to detect the presence of UV-C easily and quickly.

If you’d like to know more about UV-C light, be sure to read ‘How to Use UV-C Light Safely’.

Crystel Pang
Industrial Design Engineer