Significant efforts in academia and industry are devoted to studying and improving the resource and energy efficiency enabled by the Internet of Things (IoT). At the same time, the global pressure of humanity on the environment keeps on increasing, calling for radical changes in the organization of our developed societies. In this context, the increasing use of IoT to support smart applications in fields such as city and building management, farming, and healthcare, raises sustainability concerns as it is calling for a massive deployment of smart IoT edge devices. In this paper, we hence investigate what strategy should be used to help keeping IoT deployment within environmental limits, while taking advantage of its benefits where it is relevant. We first build on existing literature to show that improving the environmental performance of a product through conventional life-cycle assessment (LCA) and ecodesign is not sufficient to guarantee environmental sustainability. As this is a recurrent shortcoming in conventional LCA of ICT, we argue that LCA should be integrated in a broader framework, to ease the inclusion of both direct and indirect environmental effects. By exploring future-oriented studies, we show that using a backcasting approach consistent with Paris Agreement goals has far more potential than the conventional forecasting approach used in ICT studies so far.We illustrate this on the case study of smart public lighting in Wallonia, Belgium for the period 2020-2050, and evaluate the direct impacts of this real-life IoT solution through a full-scope multi-indicator LCA.