Nitor is a base item for Thaumcraft 3, and is one of the first researchable items. You can place it anywhere as a light source block. The light produced by Nitor is the same strength as that of glowstone.
"This flame seems to be fueled by magic itself. The number of uses for an everburning flame seems endless, but unfortunately it doesn't seem to produce much heat, though it could prove to be a steady source of light and energy.
Nitor can also be placed in the world to act as a magical light source."
Nitor is one of the first theories you can develop when you first start out.
Other information Edit
You can use 6 torches and 2 coal to get 1 Nitor. It will not spew into the atmosphere and generate flux.