How many clerics and wizards and illusionists you got in your world.
One 3rd level wizard can produce one continual flame a day. Thats 365 in a year, in ten years thats 3650.
Ten of them could create 36500 in ten years. Throw in some levels, some clerics and some illusionist and you could create millions of continual flames in no time at all.
But better than light bulbs as they require no electricity (wiring), no oxygen (useful underwater) and it produces no heat (potential fire damage).
Light for all the world. Everywhere! Street lights, dungeon lights, house lights, library lights, head lamps, flashlights, shield lights, sword lights, etc.
Since it can be cast anywhere.... hand, brow ridge, quill, page of a book, end of a stick, in bowl etc.
The potential uses of this are unreal.
One might even be able to light up north korea