The classic G4 low voltags haogen lamps can be found in many places. The distance between the two pins is 4mm. G4 LED retrofits save energy by a factor around 8;1. This means 8 watt G4 halogen can be replaced by 1 watt G4 LED power.Very important are the dimensions. Especially the G4 LEDs with a higher luminous flux have bigger dimensions and do not fit into all existing G4 halogen luminaires.