CPD PROGRAMME | EXTERIOR LIGHTING (possibly after some duration) impact visual performance. LED lamps generally only emit light in a 180 cone, changing the nature of the optical design from traditional exterior to cause glare than a traditional low-pressure sodium lamp that has a comparably large surface area and optic. Precise optical control glare from small sources such as LEDs. The impact that the correct optical control discomfort, discontent, and distractions for the public, but also limiting the effect of Figure 1: Categories of intrusive light (Source: ILP Guidance Notes 01/212) As noted in SLL LG06, in addition to the visual impact, there are a number of other aspects that need to be considered in the development of any external lighting design: the creation of a safe and pleasant environment; the appropriate use of energy; ease of maintenance; countering the threat of vandalism; and harmonising the appearance of the lighting equipment with its surroundings. Environmental assessments of lighting systems are necessary to determine environmental performance, reduction or elimination of the negative impact caused by lighting, energy consumption and CO2 emissions (as well as considering waste management of the lamps and luminaires). The optics of the luminaire will impact the ability to illuminate only areas that are intended, minimising wasted energy and reducing operational environmental impact. Much of the guidance on the metrics used to select appropriate exterior lighting that avoids obtrusive light derives from the publication CIE 150.4 This includes sections that consider the effects and the light parameters for residents (the public), transport system users (including road, marine, waterway and air), sightseers and astronomical observations. It includes 3 of the paper by Boyes et al see panel Lighting impacts on insects). In LG06, it is noted that there is a tendency to choose a luminaire with the highest may be an incorrect assumption. Although controlling and directing light inevitably reduces LOR, this would normally light the space more effectively because spill and lighting luminaires have optics that develop a bilaterally symmetric distribution, where the light emitted from the left of the axis is identical to the light emitted from the right.3 However, many exterior designs require that light is directed in different directions from each axis. Asymmetrical distribution concentrates the light in Boyce1 notes that, typically, advice given to reduce obtrusive light is to use a fully shielded luminaire, which emits no light directly above the horizontal plane through the luminaire. Fully shielded luminaires normally have the aperture through which drops below the plane of the aperture are not fully shielded and will emit some light The advice to use fully shielded luminaires considers the luminaire in isolation and not as part of a lighting system. This can be a problem when the luminous intensity distribution of the fully shielded luminaire is narrower than a lessconstrained luminaire, necessitating closer spacing between luminaires to achieve the required uniformity of illumination, resulting in a more expensive installation should be included when assessing potential obtrusiveness, and how variations in the impact of lighting. To assist in assessing suitability of designs, environmental lighting as the basis of the recommendations in the ILP and SLL guidance (as shown in Table 1). Issues such as brightness, direction and context need to be considered in the development of the external lighting design to ensure that light pollution and light spill is avoided. The spill of light into areas of nature, such as trees, bushes, plants, and woodland, foliage (as widely reported recently in the popular press, following the publication maximise the spacing in between each luminaire. Maximising spacing will reduce cost of the scheme (fewer luminaires purchased) and reduce energy consumption. Zone Zone description and examples of such zones EO4 Areas designated as UNESCO starlight reserves, major optical observatories E1 Areas with intrinsically dark landscapes: national parks, areas of outstanding natural beauty (where roads are usually unlit) E2 Areas of low district brightness: outer urban and rural residential areas (where roads are lit to residential road standard) E3 E4 Areas of middle district brightness: generally urban residential areas Areas of high district brightness: generally urban areas with mixed recreational and commercial land use with high night-time activity Table 1: Environmental lighting zones1 54 October 2021 www.cibsejournal.com CIBSE Oct21 pp53-56 CPD186 Tamlite Supp.indd 54 24/09/2021 17:41