Using UV-C light to sterilize the rooms of the holiday cottage, as part of a cleaning programme between guest stays has its advantages. It doesn't leave a chemical residue and doesn't increase humidity. The process is quite fast, depending on the power of the ultraviolet lamp deployed. However it is not without risk to the operators of the lamp. There are fairly strict EU and USA regulations relating to the health and safety exposure limits for ultraviolet lamps. During use you need to wear protective clothing and goggles/face shields to avoid exposure to the light.
Here's one example: Artificial Optical Radiation Directive 2006/25/EC is 30 J/m² at 253.7nm for a daily 8 hour work shift.
At a distance of 5cm, the ultraviolet light intensity of the lamp we use is around 17 milliwatts per square centimetre. This would exceed the daily safe allowance within a minute if exposed directly to the UV-V light output from our lamp. The further you are away from the lamp the intensity starts to decrease quite rapidly. The shape of the lamp reflector affects how the intensity of UV-C is distributed. Reflection from surfaces can also increase the indirect exposure. As part of the safety procedures the operator should not be in the room when the UV-C lamp is switched on, unless fully protected by UV-C PPE gear. UV-C can be stopped by fairly light protective gear, but you need to keep it away from bare skin and the eyes. The light kills virus/bacteria by damaging the DNA/RNA within the organism. You don't need your own DNA being damaged.
However it is likely that situations will arise when you need to measure the intensity of the UV-C light to make sure you do not exceed the safe limits of exposure. We purchased a specialist UV-C meter to perform these measurement and to also test the safety level of any PPE equipment that we wear. You cannot detect UV-C light by your normal senses. We test UV-C radiation levels before, during and at the end of a sterilisation session. We also document those levels. We also record our tests on PPE equipment.
We purchased a laboratory quality meter. It is a General Instruments UV512C meter. We purchased it via Cole Parmer in the UK. The following link will lead to the Philips Lighting advice on using UV-C for disinfection.
These people https://uvcdosimeters.com/uvc-100-dosimeter/ provide dosimeter dots/cards. We are currently checking price and availability.