Basically, the halakhic decisors looked for something to classify it under, on the assumption that it was obviously prohibited. The conclusion of most halakhic decisors is that it is prohibited because of creating something new, or various other possibilities. In the past they classified it as kindling, but once people moved to LEDs that was no longer possible. So according to that, it is a somewhat shaky prohibition.
Rabbi Michael Abraham brings the Chazon Ish’s view that this involves the Torah-level prohibition of building, and after all the halakhic decisors “laughed” at the Chazon Ish and made his approach irrelevant, the Rabbi דווקא proves like the Chazon Ish after a neat and clear definition of the parameters of the prohibited labor of building. It is recommended to look at the column, even if it is a bit long.