SPONSOR CPD PROGRAMME Continuing professional development (CPD) is the regular maintenance, improvement and broadening of your knowledge and skills, to maintain professional competence. It is a requirement of CIBSE and other professional bodies. This Journal CPD programme can be used to meet your CPD requirements. Study the module and answer the questions on the final page. Each successfully completed module is equivalent to 1.5 hours of CPD. Modules are also available at www.cibsejournal.com/cpd Regaining dark skies This module considers the challenges of lighting populated environments while respecting the increasing demand for dark skies In February 2023, Ynys Enlli (Bardsey Island), two miles off the mainland of north-west Wales, became the first site in Europe to receive International Dark-Sky Association (IDA) Dark Sky Sanctuary certification. This recognises the importance of the exceptional quality of starry nights and a protected nocturnal environment on what is a sparsely populated island (Figure 1). This is not an admonishment of the benefits, and the potential beauty, of artificial lighting, but a celebration of how environments can prosper with careful design and management. This CPD will consider the significant challenges of lighting the more normal, populated environments while respecting the increasing appeal of dark skies Whereas an IDA Dark Sky Sanctuary designation increases awareness of fragile sites and promotes the long-term conservation of, principally, depopulated areas, the more densely occupied world can present greater challenges. The US-based IDA reports that light pollution is increasing worldwide at twice the rate of global population growth, with 80% of people and more than 99% of the US and European populations living under a light-polluted night sky. As illustrated in Figure 2, a screenshot from www.lightpollutionmap.info, the wider impact of light pollution stretches far beyond city centres. As discussed at length in CIBSE SLL Lighting Guide 21 (LG21) Protecting the night-time environment,1 pollution from the excessive, uncontrolled, or inappropriate use of artificial light is affecting human health, wildlife behaviour, and the ability to observe stars and other celestial objects. Lighting installations on industrial and commercial sites, outdoor advertising, roadways, and conurbations all need careful consideration to ensure that the design and operation of the numerous and various artificial light sources minimise the creation of adverse conditions. Human vision during periods of darkness (normally at night) is known as scotopic vision (as explained in the boxout Human scotopic vision). LG21 notes Figure 1: The night sky as viewed from Ynys Enlli (Bardsey Island), located two miles off the tip of the Lln Peninsula, north Wales, that recently received International Dark Sky Sanctuary certification (Photo credit: Steve Porter/Bardsey Island Trust) that the impacts of outdoor lighting at night affecting human perception (which otherwise would be dominated by basic scotopic vision) can be described in terms of three principle factors: Sky glow refers to the increase in the brightness of the sky at night that overpowers light produced by natural sources, such as moonlight and the stars. Sky glow results from light that is emitted directly from a fixture, as well as light that is being reflected from the ground, from buildings or other sources. The light traverses the atmosphere, being scattered www.cibsejournal.com April 2023 41