Lden is the common EU indicator that corresponds to the average noise level throughout the day, evening and night, to which a citizen is exposed over the period of a year. Environmental Noise Directive 2002/49/EC defines a number of noise indicators to be applied in noise mapping and action planning. These indicators represent a physical scale for the description of environmental noise, which has a relationship with its harmful effects. The two most important indicators are:
1. Lden: the day-evening-night–level indicator designed to assess annoyance;
2. Lnight: the night-level indicator designed to assess sleep disturbance.