The effectiveness of UV-C light for surface disinfection is dependent on several factors, such as intensity, duration, distance, angle of exposure, type and shape of the surface, and the presence of dirt or organic matter. To optimize UV-C efficiency, you should use a device that delivers a high dose of UV-C light measured in millijoules per square centimeter (mJ/cm2). Additionally, expose the surface for an adequate length of time based on the dose and the microorganism. For instance, to kill 99.9% of the coronavirus, you need about 20 mJ/cm2 which takes about 10 minutes with a 30-watt device at a distance of one meter. Furthermore, place the device close to the surface without touching it to increase intensity. The angle at which you position the device also affects reflection and absorption by the surface. Moreover, clean the surface before using UV-C light to get rid of dirt and organic matter that can block or reduce UV-C light. Additionally, clean the device regularly to prevent dust or debris from affecting its performance. Finally, choose a smooth, flat and light-colored surface to enhance reflection and absorption of UV-C light while avoiding surfaces that are rough, curved or dark-colored as they can create shadows or absorb the light.