Day–evening–night noise level

The day–evening–night noise level or L_den 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.

L_den is calculated as:^[5]

${\displaystyle L_{\mathrm {den} }=10\cdot \log _{10}\left({\frac {1}{24}}\left(12\cdot 10^{\frac {L_{\mathrm {day} }}{10}}+4\cdot 10^{\frac {L_{\mathrm {evening} }+5}{10}}+8\cdot 10^{\frac {L_{\mathrm {night} }+10}{10}}\right)\right)}$

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 L_den can be considered a weighted average of the yearly individual noise level during day, evening and night.

• Environmental noise directive
• Day-night average sound level, the US equivalent

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