Mike Simpson reviews the SLL's latest guidance on obtrusive light. Peter Boyce, the author of the SLL's Guide to limiting obtrusive light, is a well-known academic in the lighting profession, and brings together both research and practice to the guide, making it a one-stop shop for all issues relating to obtrusive light. For those for whom this is a new topic, the definitions of the different sources of obtrusive light - sky glow, light trespass and glare - will be useful. The guide then goes on to look at the science behind these. For sky glow, the mechanisms of light scatter are explained and the implications when light is emitted around the horizontal. Understanding these principles will enable the designer to choose the correct equipment and apply it in such a way as to minimise sky glow. The mechanisms of glare are also discussed and, although later on limiting intensities are quoted, I always have the feeling that any source against a night sky is going to cause some objection and, with something so subjective, is this the best way of controlling it? Practical measures to restrict a direct view of the source from a distance may well be the best approach.
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