What is the shape of the curve? As noted, a function is easy in XOD. For LEDs, I suspect a exponential curve?
Someone asked a similar question: Look-up tables?
I think XOD does not have good nodes for tables (I don’t see any nodes for “lists”?). You could do a table pretty easily with a c++ node.
Have you considered using “IOT” for configuration? We do this for a piece of equipment: it asks some IOT server for configuration, including tables. We use Adafruit’s IOT. Here’s some tutorial: Reading JSON Data — XOD