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SLL publishes new Guide to Limiting Obtrusive Light

The Society of Light and Lighting (SLL) has published its new SLL Guide to Limiting Obtrusive Light.  This publication meets an important need to further understanding in the controlling of obtrusive light and the design implications for outdoor lighting. 

While outdoor lighting is important for people's work, safety and leisure, it can cause issues of sky glow, light trespass or glare. Different people give different priorities to these effects, but obtrusive light can affect health if sleep is disturbed, and affect the visibility of the stars and the behaviour of flora and fauna.

There are a number of methods for limiting obtrusive light - the most effective is not to have any, so this means carefully considering if outdoor lighting is necessary.  SLL's Factfile 7: Design and Assessment of Exterior Lighting Schemes provides a structure to assist with such an assessment.  Given that outdoor lighting is needed, how much light is required?  The greater the amount of light used, the greater the risk that obtrusive light occurs.

This outcome has critical implications for planning, design and specification of exterior lighting schemes.  The new SLL Guide provides further insight into the factors and considerations around obtrusive lighting within each of these responsibilities.

Planners will need to consider the environmental zones such schemes are used within and the lighting criteria for each.  These criteria are a maximum upward light to limit sky glow, a maximum illuminance on windows to limit light trespass and maximum luminous intensity to limit glare. At any specific site consideration has to be given to the need for the proposed lighting.  The times of lighting use also need to be considered and options for the use of a curfew.

Specifiers will also examine the purpose of the lighting and widely recommendations for road lighting, for work outdoors, for sports and for security lighting.  These are recommendations applicable regardless of location because they are based on what is required to carry out tasks associated with the location.

Controlling obtrusive light requires careful design.  A comprehensive approach to quantifying obtrusive light using software has been developed called the outdoor site-lighting (OSP) method.  It allows lighting designers to model the location and magnitude of illuminance and problems that can occur, but not what the solution might be.

The new SLL Guide offers simple processes for developing a lighting design for a new installation and for assessing existing designs where there have been complaints of obtrusive light.  In addition it offers some solutions to applications where obtrusive light is common but could be reduced easily.

Both the new SLL Guide and Factfile 7 aim to encourage the use of a balanced approach to achieve a high quality lit environment that all can enjoy and benefit from.

The Guide is available from the CIBSE Knowledge Portal here