**5. Conclusions**

In this work, we considered how modernization of HPS-based lighting installations influences CO2 emission volumes related to urban roadway lighting. CO2 and other greenhouse gases emissions are linearly dependent on the energy usage so a parallel analysis of both was made. Our study relied on the real-life case of the retrofit made in the city of Cracow.

In our research, we show that:


The presented work links well defined, quantitative analysis of financial aspects of a public lighting retrofit investment with considerations on environmental influence of such a modernization. This link is obtained thanks to assessing the money savings corresponding to a reduced CO2 emission. Thus the environmental impact can be included quantitatively in the retrofit strategy planning. Moreover, for investments financed in the ESCO (Energy Service Company) model [28,29], we show that a payback period can be shortened by 9% (or even more, taking into account the current trend of the EUA price) thanks to incomes achieved due to the reduced CO2 emission.

**Author Contributions:** Conceptualization, A.S.; Data curation, A.B.; Funding acquisition, A.B.; Validation, A.B.; Writing—original draft, I.W.; Writing—review & editing, A.S.

**Funding:** This research was funded by The National Centre for Research and Development gran<sup>t</sup> number POIR.01.01.01-00-0037/17-00.

**Conflicts of Interest:** The author declare no conflict of interest.
