Diode Dynamics 39mm HP6 LED Bulb LED - Blue (Pair)Features Direct replacement for factory 39mm festoon bulb Increased output with LED appearance Plug and play simple installation Overview Design. The 39mm HP6 LED bulb is a direct replacement for any 39mm size bulb commonly found in door lights dome lights and trunk lights in many vehicles. Populated with eight high power LEDs arranged in an omnidirectional pattern the HP6 upgrades the factory yellowish incandescent bulb to a more modern LED