Hi Odrene,
A very quick perusal of the net reveals the following [historic] figures. So, don't worry about climbing up a ladder, checking the type and wattage of the bulbs, monitoring the number of hours in use and applying some obscurantist schoolboy sums


to prove that a circle is a sorta 'roundy' thing. Sit back, chill out, make a cuppa and surf the net. Why keep a dog and bark!? Your question is a very reasonable one
How much does it cost to run an average UK street light per annum?
1. I can confirm that there are 20,537 street lights in Scottish Borders Council area.
2.
It cost £27.40 to power each street light in 2010.
3. The Council has spent £563,700 on electricity for street lights in 2010/11 to date.
4. It cost £334,142 to maintain/repair street lights in 2010/11 to date.
5. On average it costs £66 to maintain a street light for a year.
6. It cost £28.03 to power each street light in 2009.
7. In 2009/10 it cost £546,663 to power all of the Council's street lights.
8. The maintenance costs of street lights in 2009/10 were £327,156.
9. The cost of running street lights in 2011 has risen.
How much does it cost to run an average IRISH street light per annum?
The answer is
I personally can not give you the definitive answer! However, the above figures from THE SCOTTISH BORDERS COUNCIL are a good starting point in guesstimating the unit costs here in IRELAND in 2017. My guess? says €75/€100 per unit per annum, but there again, I don't gamble
Hopefully a Lighting Engineer or other qualified person will provide the metrics.