Light nuisance, if we cannot practically measure intensity how do we assess a nuisance complaint?

Over the past weeks I have been discussing the measurement light nuisance with Carl Gardner the editor of the ILP’s lighting journal.

Essentially light nuisance is defined as two issues, the first is the vertical illuminance onto a window and the second is the intensity of the light towards an observer within their premise. The limitations for these are given with CIE 150: ‘Guide on the limitation of the effects of obtrusive light from outdoor lighting installations’ and the ILP’s own document ‘Guidance on the reduction of obtrusive light’’ which is essentially a distillation of the detailed CIE Standard.

Vertical illuminance (lux) is easy to measure and just requires a suitable calibrated illuminance meter, intensity (cd) however is very difficult if not totally impracticable to measure and an illuminance meter (cd/m²) cannot be used for this purpose.

In saying this measurement of intensity may be achieved by the masking of the illumination meter by a matt black tube, say a section of drainage pipe with small holes at each end aimed at the light source. The intensity can then calculated by multiplying the measured illuminance by the distance squared. This approach is prone to many errors and really is not practicable especially if you are looking to complaints regarding sources some distance away.

So how can we effectively look to measure any complaint of lighting nuisance if one of the key aspects cannot effectively be measured in the field? We can look to model it within software such as Calculux but that will require all of the ‘as installed’ installation details of the scheme to do this and again this is not practicable to collect so we are at an impasse, we have a defined limitation which causes compliant but cannot be measured.

A practical solution may be to redefine the glare aspect of nuisance in terms of luminance and then a suitable luminance meter could be used but would this be right?

And there it ends really, what do we look to do, if you are interested in discussing please comment within this Blog or alternatively please go to Linked-In where a discussion has been opened under the Lighting Designer Group following on from recent discussions within the group on sky glow.