Surely we have all already seen a multitude of systems that promise to disinfect all types of environments against Covid-19, especially when we talk about time control such as the Biometric Clocking. And one of these technologies is Ultraviolet Rays. We are going to try to clarify what this consists of and what are the hoaxes that will try to strain us

What are they? Ultraviolet rays are LIGHT, but of a color that our eyes cannot see. The sun also produces them but they are attenuated by the Earth’s atmosphere, although at higher altitudes they are less attenuated and more intense

How do they fight microorganisms? This type of light is only effective as a germicide if its COLOR is exactly the one corresponding to 270 nanometers. Light of that wavelength (of that color) has the ability to break the DNA / RNA chains of living organisms and is called UV-C (Ultraviolet type C). This color is NOT VISIBLE to the human eye. If they show you purple lights, those devices are generating colors that are not effective as germicides.

What is the necessary dose for my Biometric Clocking? This depends on the power of the light generator. Also the distance to the surface to be sterilized (remember that the power decreases exponentially with distance). And finally the TIME during which this light is applied. If the equipment that generates the light distributes it in a multitude of colors, we will surely see some of them as violet. In that case we will be wasting energy and only the fraction of UV-C that is generated will be effective as a germicide.

Has its effectiveness been proven? For each type of microorganism a different dose is needed to destroy it. This dose depends on the power, distance and time. There are programs that calculate the necessary dose in each case. Data are not available for Covid-19, but for some similar viruses such as influenza, bacteriophages, hepatitis and polio that are very sensitive to UV-C light. Others like the tobacco mosaic are very resistant and need very high doses, but they are very different viruses

Are they dangerous for people? If we are using doses to eliminate germs, viruses and bacteria, we will also have adverse effects on any living tissue. NEVER look with the naked eye at a UV-C generator of any kind. Also do not apply them on the skin

How can we protect ourselves from UV-C? UV-C light must be confined within the equipment that generates it and be activated only when there are no people present. The good news is that UV-Cs are very easily attenuated as soon as they have to pass through any material other than quartz. A simple sheet of clear plastic blocks and attenuates them tremendously


The objective was to sterilize the surface of the fingerprint sensor in the Biometric Clocking. The system had to work automatically applying an adequate dose of UV-C on the sensor after each use. This implies a delay between users and we have had to use a UV-C generator type LED but with sufficient power so that the application time of the dose is as short as possible. For this we have used a device from the Luminux house with a 60º quartz lens that provides a radiation flux of 40.81 mW.

At Vigilant, we have designed a housing that covers the fingerprint sensor and in which the UV-C LED is installed at the top, illuminating the entire surface of the sensor at a distance of 24mm. An aluminum substrate PCB has been used to dissipate the heat from the LED.

fichador biométrico - Desinfección automática por ultravioleta tipo-C - control horario - Vigilant

A capacitive sensor detects the presence of the finger and only activates the UV-C generator when the finger is removed to provide maximum safety for users.