G24d 4 pin bulbs - the 'd' is for double pin. G24d PL lamps are available with either a double or triple turn tube. Each 'turn' is one u-shaped glass tube.
Triple turn bulbs (GX24d) usually have a hexagonal lamp base.
These lamps are not often interchangeable between different wattages. Each wattage has a different key location. These are plastic tabs located around the lamp base. The number after the 'd' (1,2,3,4, or 5) indicates the key used.
