To safeguard and enhance the night time environment it is necessary to control obtrusive light (also known as light pollution), which can present physiological and ecological problems to surroundings and people.

It is possible that in some circumstances obtrusive light may be considered a statutory nuisance as set out in section 102 of Clean Neighbourhoods and Environment Act 2005. (The act is available at www. opsi.gov. uk). The act does not make it clear under what conditions lighting becomes statutory nuisance but it does list a number of situations that are exempt.

The limits of obtrusive light for exterior lighting installations, to minimize problems for people, flora and fauna, are given in the table below , whilst the values below are not taken from the 2005 act they represent good practice and so may be used as a starting point when trying to apply the law.

Zone	Light on properties		Luminaire Intensity		Upward Light	Luminance
	pre curfew (a)	post curfew	pre curfew	post curfew		building facade	signs
E1	2	0 (b)	2.5	0	0	0	50
E2	5	1	7.5	0.5	0.05	5	400
E3	10	2	10	1.0	0.15	10	800
E4	25	5	25	2.5	0.25	25	1000

(a) In case no curew regulations are available, the higher values shall not be exceeded and the lower values should be taken as preferable limits.
(b) If the luminaire is for public (road) lighting, then this value may be up to 1 lx.

E1 - represents intrinsically dark areas, such as national parks or protected sites
E2 - represents low district brightness areas, such as industrial or residential rural areas
E3 - represents medium district brightness areas, such as industrial or residential suburbs
E4 - represents high district brightness areas, such as town centres and commercial areas

	is the maximum value of vertical illuminance on properties in lux
	is the light intensity of each source in the potentially obtrusive direction in kcd
	is the proportion of the flux of the luminaire(s) that is emitted above the horizontal, when the luminaire(s) is (are) mounted in its (their) installed position and attitude
	is the maximum average luminance of the facade of a building in cd/m²
	is the maximum average luminance of signs in cd/m²

We recommend Megatron DL3/LC or Megatron DL3-5266 for measuring obtrusive light.