deriv LSK ETT STT aSTA ALPH OLDHOMEPAGE NEWHOMEPAGE
The vowel L ऌ appears only in some derivatives of the root kLp क्ऌप्, such as kLpta- क्ऌप्तॱ "ready, prepared". In grammar commentaries you can also find the word LkAraH ऌकारः, meaning "the sound L ऌ". And that's all.
It is heavily suspected that in /pANini's times L ऌ was pronounced like R ऋ, but with the tongue narrower, the same way it's narrower in l ल् than in r र्.
However, nowadays it is traditionally mispronounced as lR लृ.
This mispronunciation would screw up the verses in which a short vowel comes before kLpta क्ऌप्त, so feel free to say kRpta when chanting verses, as a lesser of two evils, rather than klRpta.
Wikipedia on HK says that you are supposed to type L ऌ in Roman as "lR", same as if it were lR लृ. I use "L" in this website, however.
See also long L.