Bulb Without Filament . The purpose of the outer envelope is to isolate the user from the mains voltage present on most led bulbs and to make them mechanically compatible with normal a65 or similar incandescent bulbs. Filament cooling unlike what others have said, you don’t want to cool the filament at least not with a gas in the bulb, but you would like to keep oxygen away. 4 Watt 12 Volt Candle Dimmable LED Filament Bulb (E27) LiquidLEDs from www.liquidleds.com.au In 1913, irving langmuir figured out that placing an inert gas like nitrogen inside the bulb doubled its. 300 lumens isn't even close. How many filaments are there in a bulb?