**4. Discussion**

Several comments related to the above analysis have to be made.

Volumes of GHG emissions presented in the previous section may be slightly different for other countries due to different structure of energy sources (see [25]) and different emission factors. For example, countries with an overwhelming share of nuclear plants in the total electricity production can have a lower CO2 emission factor than countries where most electric energy is produced in the coal plants.

As mentioned previously, although lighting class and luminaire power structures of the considered case (see Figure 2) are sufficiently representative for the presented analysis, one has to keep in mind that such an extrapolation estimates results rather than gives the precise values. Regardless, those numbers give a reasonable measure of an overall reduction of a GHG related pollution in the scale of the entire city.

The results shown in Figure 5 correspond to the roadway structure of the city of Cracow and may be subject to changes for a city having a different road network structure. Additionally, municipalities can apply other lighting class assignment policies resulting in dominance of high or low energy demanding classes.

A highly important issue for authorities planning lighting retrofit works are investment costs. One has to be aware that a final decision on retrofit strategy is usually a trade-off between financial constraints and other, non-fiscal (from the investor's perspective) factors such as environment protection. The presented results shed light on how the latter can be taken into account when assessing an investment's financial profitability.

In the presented considerations, we did not discuss maintenance costs of a lighting installation. They are another factor which leads to choosing LEDs [26]. It is worth mentioning that the total maintenance cost savings achieved thanks to upgrading 300 fluorescent tubes with 100 ballasts to

LEDs is over \$ 16,500 over an LED lifetime. For the case of HIDs, upgrading 100 bulbs to LEDs yields over \$45,000 of the total maintenance cost savings, over an LED lifetime [27].
