LED vintage Edison bulbs are slowly becoming a growing trend in homes, restaurants, and other commercial interiors. These classic styled bulbs preserve the look of the Edison incandescent bulb, and provide a nostalgic throw-back. But have you ever wondered how the beautifully constructed filaments inside the bulb were made? Also, the bulbs are LED, but where are the tiny diodes?
The first LED filament bulb was introduced in 2008 by Ushio Lighting. The original filament bulb did not generate popularity due to poor thermal dissipation and lack of light dispersion. As improvements were made to the design, LED filament bulbs were, and still is, slowly being adopted into the North American market. Why such a slow progression? There are currently only two filament LED manufacturers that are UL-certified. And only one of the two manufacturers, AXP Lighting, is both UL- and Energy Star- certified.
So how has LED filament bulbs improved since its creation?
Greater light dispersion. LED filament bulbs are now omnidirectional, meaning they can transmit light in all directions—360°.
Chip-On-Glass (COG) filaments. The tiny LED chips are mounted on a transparent substrate, made of glass and sapphire material, rather than metal. The transparency of the substrate allows for light to disperse uniformly—transmitting light in all directions.
Phosphor covered filament. The filament is covered in a silicone & phosphor resin which changes the blue LED light to white. The resin also allows for a more accurate color temperature control for lamp makers.
Thermal management. The dissipation of heat from LED filaments is now more than just utilizing bulky heat sinks. The most ideal method of heat management is a high voltage – low current design. To make thermal management more effective, multiple dissipation paths can be applied. Understanding and using the “Droop Effect”—the LED decay rate in correlation to junction temperature—is one additional method. Using special gas mixtures inside the glass lamp to facilitate heat transfer to the glass surface more efficiently is another method. Lastly, a more creative method is by arranging the filaments in a way that will dissipate heat without sacrificing omnidirectional light.
Take a look at the filament arrangements below. AXP Lighting is located on the right. Their patented cross filaments provide a “center of light” with 360° dispersion. The bulb on the left has a “tree” type filament design.