My recipe calls for crystal malted grains and a website I found offers a large choice from 10L to 120L Breiss, what is the difference between "L" designations?
It's the lovibond scale. The higher the number, the darker the color it adds to your brew and the less fermentable sugars. 10L is very light and 120L is very dark.
It's not just color, there's a huge difference in flavor between the various lovibonds. 10L gives a basic sweetness, while 120L gets into raison-ey, dark-fruit kinds of character. Darker colors will give more of a caramel flavor.
Some old recipes will just call for "Crystal Malt," in which case a 40L is a pretty common choice.
At this point I am taking what I can find online! I have only really found one store that has a good well rounded selection from grains to malt to hops, etc.