What is it?
PL or PL lamp, is a term used by the aquarium hobby to to identify a particular type of compact fluorescent Lamp made by the Philips Lighting company.
The correct term is PL-S and is a 2 pin G23 (or GX23) base with a twin finger lamp.
Colour temperature is : 2700K, 3000K, 3500K, 4100K or 5000K
Typical life is ~10,000 hours.
Data file for these lamps is available from the Philips web site - See here