Code:
"Light": {
"VanillaLightId": 3,
"Radius": 0.5,
"Color": { "R": 255, "G": 255, "B": 255 }
All you should have to do is edit the line with "VanillaLightId". You'll want to change the 3 out for "sconceLight" in quotes, so that it looks like this:
Code:
"Light": {
"VanillaLightId": "sconceLight",
"Radius": 0.5,
"Color": { "R": 255, "G": 255, "B": 255 }
Stardew changed how it wants mods to reference these, so SMAPI either won't load them, they won't light up, or they'll outright crash the game. Thankfully, so far it's been SMAPI-skip.
This is related to an edit I had to make in the Custom Critters code core, which was one of the reasons SMAPI was skipping it. Not a lot of the critters themselves use being a light source, so not a lot need the fix. It compiled okay with the critter included, and I
think I've had more fireflies in summer again without crashes, but I haven't had a lot of playtime to test just it yet.
I can troubleshoot further if it still just doesn't work-- the fireflies are my favorite!