As already mentioned, the spotlights are more likely to be a limelight or an equivalent, which are essentially gas torches directed at quicklime to produce an intense light that can then be directed as spotlights. No electricity is required.
In regards to Mrs. Colline, I understand that she probably warranted her ultimate punishment for the setting, but I feel it's out of tone for the manhwa. It's such a fluffy piece about an overworked woman trying to enjoy her tea. Having someone executed then it moving on quickly to a love scene is strange to say the least. If they're going to have Mrs. Colline die, at least make it a serious issue, rather than having it pass by like used tea leaves.
I also don't understand as to why Mrs. Colline's backstory was somewhat shown in a sympathetic light, yet there being no resolution or even further acknowledgement of it. It's clear that if Mrs. Colline's circumstances were briefly altered, she'd not have turned out to be such a villainess. And we even knew of Mrs. Colline's motive; she did not intend to have Chloe killed, she only wished for her to be disfigured. It's not at all any nobler, but it was clearly not a purposeful attempt at murder.
Alas, I guess it's glossed over quickly enough, but I definitely tasted a bit of the bitter tea leaves in this cup of tea.