The commonly used
value of n for the n-percent exceeded level, Ln,
are 10, 50, and 90.
L10 is the level exceeded for 10%
of the time. For 10% of the time, the sound
or noise has a sound pressure level above L10.
For the rest of the time, the sound or noise
has a sound pressure level at or below L10.
These higher sound pressure levels are probably
due to sporadic or intermittent events.
L50 is the level exceeded for 50%
of the time. It is statistically the mid-point
of the noise readings. It represents the median
of the fluctuating noise levels.
L90 is the level exceeded for 90%
of the time. For 90% of the time, the noise
level is above this level. It
is generally considered to be representing the
background or ambient level of a noise environment.
For a varying sound, L10 is greater than L50 which in turn is greater than L90.
The following graph illustrates L10,
L50 and L90.