Normally, the displays with 14 pins do not have a backlight and the Optrex data sheet says it doesn't have one either. Ones with a backlight have an extra pin 15 and 16 to supply it. However, the PCBs are usually made with provision to fit a backlight as an option so perhaps the pads you see are for that but not actually used.
The backlights are typically either electroluminescent (~100V AC) or more commonly LED in which case it will be a single white or green LED needing around 5V but you might have to externally limit it's current to around 10mA or less.
Brian.