Gabriel

As to candle offerings as a sacrament, there is discussion in catholic sunday papers and magazines here once in a while, like if there is a real living flame to sacrifice a wax offering needed or if it is a purely symbolic act that requires mostly the person offering up a light for their departed or somesuch should better just feel the sacrifice in the purse in our times, like in the way the meatless friday fasting requirement was eventualy reformed.... if so, the temporary light in front of the picture of a saint is just a reminder an offering was given, not the offering itself. But one thing seems inevitable, to ban household parafine candles from churches for they are potentially unhealthy to humans and especially bad for oil paintings and such, asides from those conservative priests that claim that they do not really fulfil a requirement of purenes that was written somewhere in the time of the church fathers and that can only be reached with purified best grade plant oils and wax from bees that where the cleanest and pricyest lightsource since the earliest cultures and really consumd by a true flame...

Of course for poor and less educated catholics asking a saint for help at a shrine this all is not really of any interest. All they want are graveyard candles and long novena lights they can afford and that look preferably close to the ones their forebearers had used.
Myself I had a very religious catholic grandma that bought plain subventioned parafine household candles in stock at the drugstore meant for power outages and the priest blessed them in the mass for a few extra hellers, but she lived in a comunist country without legal devotionalia stores, the stukko in her church was blackened and came almost down anyway as the comunity had no saecular help at all with roof repairs for cultural means (will say, they could not even get scaffolding if raising a fair wage for a specialist as all the handymen worked in state owned building companies and had no tools and materials to come buy for weekend labour), and her son, the well doing citizen of western Germany, admonished her severely when she gave any of the hard currency he slipped to her during visits to the priest instead of using it for her own convenience and comfort as her regular life standard was so much lower than ours.
But she waddled to church each sunday from Modlesovice to Podsrp in spite of the weather and all the water in her swollen legs and no propper orthopedic footwear, and she lit a candle after mass at the image of the Lady of Sorrows and prayed, as she thought it would help with her everyday issues and the purgatory status of deceased family members and all that.
So you see, I can understand simplicity and cheap offerings piling in ramshakle chapels and shrines of poor rural people but I can not romanticize it all that much. If they feel better from praying and offering candles, its good for them, but in a perfect world such a setting for feeling better would not be required.
I am quite happy to report the baroque village church that was in the 70s and 80s in such an awful shape looks really quite good now, with no black ceiling at all any more, but the grandma herself died several years before the velvet revolution and never saw it look that great. Not all is great in the Czech Republic today and I certainly had higher expectations back in Vaclav Havel's lifetimes for the country to develop, but the little church is saved and profesionally renovated, shiney and clean like many baroque buildings in the old villages are by now, oozing out the cheery naive Josef Lada village flair for tourists coming trough.
Here you can see Our Lady of Sorrows Church at Podsrp as it looks today (reading about it is an other matter, my own czech is much to bad to understand and translate anything written there): https://www.farnost-strakonice.cz/kostel-panny-marie-bolestne/