Exemptions for LEZ aim to ensure that all vehicles meet a certain emission standard, rather than reducing the number of vehicles entering the area per se like a LTZ does. There are a few exemptions for those vehicles that do not meet the standards, but there are good reasons for allowing them access, for example emergency services, rarely used very expensive vehicles.  A complying vehicle wanting to enter the LEZ often has to identify itself as complying with the standards, either by showing a sticker, or being on a database (usually automatically on a national vehicle database plus those actively registered (foreign) vehicles that are not on the national database). These are not seen as permits, but stickers or registrations. (see also Permits for Low-Emission Zones)