how often can an experienced lder have an ld ?
Appended “(regarding LD frequency)” to the title for clarity. 
Theoretically you could have an LD any time you are dreaming, so every night would probably be the best answer to that. Although there are very few people that have them that often.
Well, I think it also depends how many REM cycles you go through. I once had 5 LD’s in one night… but that was a very odd occassion!
It takes a lot of practice and patience if you’re not a natural Lucid Dreamer, but I don’t see why anyone isn’t capable of achieving at least one every night after lots of practice and time!
Good luck and 
to the forum!
You can have a LD every time you dream.
And it´s not so hard either ^^
You just have to put your mind to it.
its not like it´s running a marathon, you never get tired of it…