You must change the UV lamp in your UVC device every year, even if it's still working, it simply no longer emits the correct UV rays. Depending on the model of your UVC device, it may contain either an energy-efficient PL lamp, a T8 TL lamp, or a newer generation T5 TL lamp. Take the old lamp with you to the store to avoid mistakes. Also, be sure to clean the quartz glass of the device to ensure proper radiation.