Legacy Dynamic Lighting (LDL) is a catch-all name referring to the old Roll20 systems of Dynamic Lighting and Advanced Fog of War.

Updated Dynamic Lighting(UDL) is the name of the new lighting system released April 8th 2020, which will exist in parallel with LDL until feature parity, bugs are fixed, and people have had time to adjust things to the new system.

In UDL, the features of old "Advanced Fog of War" have been renamed as Explorer Mode to avoid confusion.