The G9 and G4 LED bulbs derived their significance from the types of pins used. The arrangement of the pin is the most important part from which we can differentiate both. The LED lamps have both the pins placed together which prevents them from getting interchanged with bulbs of high power. This prevention is necessary to avoid the excessive heating of the lamp which might even lead to a fire in the worst case scenarios.
LED Lights gets less heated as compared to that of the incandescent bulbs, however, these G4 bulbs and G9 bulbs help in maintaining the proper safety. The diameters, usage and the size of both the types differ. The G4 LED lights generally have 4.0 mm pin placed centre to centre with a diameter of 0.65 - 0.75mm. The G4 LED bulbs are used in small bulbs of 5/10/20 watt and 6/12 volt. In G9 LED lights have the pins placed at 9.0 mm centre and are used in the LED lamps.