Tiny update. I had someone request an option to make light sources only work when held (in the main hand as there is currently no way to make them work in the off hand). I added a way to toggle this feature on.
By default addon will work as it always has (in inventory, along with the thick potion interactions).
If a playert goes in to creative mode and puts an awkward potion in the main hand, after 15 seconds, the player will receive a message you are now in hard lighting mode. where only lights in the main hand work.
To turn this off hold on to a mundane potion and wait for the message (the check is ever 15 seconds). You only get the message if the mode changes.
You can leave creative mode after you have the game set the way you like and it will stay that way.