From the scientific point of view the best criterion for choosing a noise indicator is its
ability to predict an effect. Therefore, for different health end points, different indicators
could be chosen. Long-term effects such as cardiovascular disorders are more
correlated with indicators summarizing the acoustic situation over a long time period,
such as yearly average of night noise level outside at the facade (Lnight,outside)1,
while instantaneous effects such as sleep disturbance are better with the maximum
level per event (LAmax), such as passage of a lorry, aeroplane or train.
From a practical point of view, indicators should be easy to explain to the public so
that they can be understood intuitively. Indicators should be consistent with existing
practices in the legislation to enable quick and easy application and enforcement.
Lnight,outside, adopted by the END, is an indicator of choice for both scientific and
practical use. Among currently used indicators for regulatory purposes, LAeq (Aweighted
equivalent sound pressure level) and LAmax are useful to predict short-term
or instantaneous health effects.
SLEEP TIME
Time use studies, such as that undertaken by the Centre for Time Use Research,
2006 (www.timeuse.org/access/), show that the average time adult people are in bed
is around 7.5 hours, so the real average sleeping time is somewhat shorter. Due to
personal factors like age and genetic make-up there is considerable variation in sleeping
time and in beginning and end times. For these reasons, a fixed interval of 8
hours is a minimal choice for night protection.
Though results vary from one country to another, data show (see Fig. 2 as an example)
that an 8-hour interval protects around 50% of the population and that it would
take a period of 10 hours to protect 80%. On Sundays, sleeping time is consistently
1 hour longer, probably due to people recovering from sleep debt incurred during the
week. It should also be borne in mind that (young) children have longer sleeping