IBSE TM40 | PERFORMANCE CRITERIA Performance Assessment Individual or organisation. For example HR, bespoke output Cognitive performance Task, bespoke tests or self-reported Control group Sustained or short-term? Large and representative? Know inuential IEQ factor or proxy or umbrella? Clearly dened and measured? for example daylight, views out Range within guidelines or beyond IEQ factor Figure 2: Studies on indoor environmental factors v cognitive performance: tips on what to look out for Advances in our understanding of nonvisual effects of light on our health and alertness have prompted much debate limits (COSHHH WEL) to prevent high CO2 levels leading to headaches, dizziness, confusion and loss of consciousness (5,000ppm for an eight-hour exposure and 15,000ppm for a 15-min exposure). Many studies on the impact of indoor air on cognitive performance focus on ventilation rates, which makes it difcult to attribute changes in cognitive performance to CO2 levels on their own, as a range of other factors may vary with ventilation. However, recently a small number of studies have ensured that CO2 levels were the only variable by keeping ventilation rates and all other parameters the same, and simply introducing higher CO2 levels into the supply air. Most but not all tests show an impact on cognitive performance at increased CO2 levels, in particular on decision making, indicating that CO2 has an impact in its own right, and at lower levels than may have been assumed in the past. However, it is also important to note that the levels at which signicant effects are reported are well above existing best-practice guidelines, in the range of 750 to 900ppm. Another very active area of research is circadian, or human-centric lighting, where advances in our understanding of the non-visual effects of light on our health and alertness have prompted much debate about what the right metrics and levels should be. There is a general consensus that traditional measures of light, such as illuminance, are inadequate to represent the non-visual impact of light, and new metrics are, therefore, needed. However, what these new metrics should be is still debated because of the complexities of our responses, interactions between different light receptors in our eyes, and time factors, which mean that a single light condition is not linked to a single response. There is no wide consensus yet; in the meantime, good design principles should be followed by seeking to give priority to daylight and views out (with glare control). It should be completed by electric lighting, which again should follow guidance from the SLL, including on parameters such as spectrum distribution, colour rendering and products. Finally, an important conclusion from the evolving knowledge is that, in current projects, we should follow the precautionary principle to avoid unintended consequences, as those mainly only manifest themselves in the long-term as in the case of asbestos and lead paint. This does not prevent innovation, but encourages a cautious review of claims, and possible effects, with monitoring and evaluation to keep new uses under review. CJ 6 June 2019 www.cibsejournal.com CIBSE Jun19 pp04-06 TM40 Supp.indd 6 24/05/2019 13:39