I would start here:

http://www.centralsemi.com/PDFs/sele...t_is_a_cld.pdf


A Current Limiting Diode, also known as a “Current
Regulating Diode” or a “Constant Current Diode”, performs
quite a unique function. Similar to a zener diode,
which regulates voltage at a particular current, the CLD
limits or regulates current over a wide voltage range.