While testing the RTX beta, I downloaded the provided NVIDIA RTX resource packs (HD Decorative and HD Foundational) to create my own worlds while testing the capabilities of RTX. While exploring some caves, I ran into a patch of lava which did not emit any sort of light. I tested both NVIDIA resource packs, and then used both the MuddleRTX and RazzleCore RTX resource packs provided by Razzleberries, and in both the lava emitted light as normal.

Attached are screenshots of the same pool of lava using each resource pack, and the attachments are named according to the resource pack used. I hope this is helpful in some way!