ILP publishes new Guide to obtrusive light

Fresh out of the box for 2020 is the revised Guidance notes for the reduction of obtrusive light, from the ILP. The original document (GN01) dated back to 2011, when the lighting world was a very different place and the LED was still making its play to become the dominant light source on the planet.


There is a different tone to the new document. GN01:2011 read like a guide to an intelligent idiot to help them with this strange idea of having lighting outside. It was sensible and practical, and there weren’t too many numbers to confuse the innocent. This new document states its case very early on:

This guidance note has been revised to reflect the changes in international guidance regarding obtrusive light as detailed in CIE 150:2017 Guide on the limitation of the effects of obtrusive light from outdoor lighting installations.


Getting CIE involved is a bit like taking your big brother into the playground when your mates won’t let you have the ball; no doubt that it seems a good thing to do, but there’s an aloofness to the new text that seems to suggest that everyone knows this already and the Guide is just there as a crib sheet. In other words, your big brother doesn’t see why you shouldn’t be able to sort all this out for yourself.

But, big brother or no, don’t imagine you can get away without reading this new edition – and then knuckling down to some serious homework before you can be confident in your exterior lighting design. As you might expect from CIE, the Guide doubles-down on the numbers and the performance criteria. Some of it is familiar; other stuff is brand new and reflects what’s been going on in the world of exterior lighting over the past decade.

As if working to a CIE framework isn’t enough, this new Guide reminds us of how government has flexed it’s muscles since 2011 and has come up with the National Planning Policy Framework, against which local planning authorities (LPAs) have produced their own design criteria. These criteria will likely include more detailed information on such things as lighting in Dark Skies environments.

This is all very important stuff and if it means that your head’s going to hurt just a little while you work out the apparent surface area of a light source as seen from the observer position, then so be it.

Let’s remind ourselves of two things: why and how we do it:

Good lighting practice is the provision of the right light, at the right time, in the right place, controlled by the right system


For your copy of the Guide, click on the logo below:

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