The day–evening–night noise level or Lden is a 2002 European standard to express noise level over an entire day.
It imposes a penalty on sound levels during evening and night[1] and it is primarily used for noise assessments of airports, busy main roads, main railway lines and in cities over 100,000 residents.
[2][3][4] The penalty for sound production during evenings and nights is due to higher nuisance perception during quieter hours and to prevent sleep deprivation for nearby residents.
Where the long-term average noise levels are defined as: The exact hours of the three periods may be chosen differently by individual EU member states.
The formula for Lden can be considered a weighted average of the yearly individual noise level during day, evening and night.
This article relating to European Union law is a stub.