You have to change the UVC lamp of your UVC device every year, even if it always works without a doubt, only it no longer diffuses the right UV rays. Depending on the model of your UVC device, it can contain either an PL economical lamp, a TL T8 lamp or a T5 lamp of the brand new TL generation. Take the old lamp with you at the store to avoid being mistaken. Please note, also clean the quartz glass of the device so that the radiation is not hampered.