I first saw these filament-type LED components in a candelabra-base bulb at the 2011 LightFair, and the company exhibiting it didn’t want me to take a photo of it. This year they were all over LightFair, although I’ve yet to see them for sale at a retail store in the US. (That will change: One lighting vendor told me that they had recently signed with Restoration Hardware as a distributor.) As far as I know, all of the filaments are made (that is, packaged) in China where low-power LEDs are plentiful.
The most common use of the filaments is in retro-style bulbs: clear bulbs that allow the “filaments” to be seen. These look particularly good in flame-tip chandelier bulbs. While the look may appeal to many as a throw-back to old-style incandescent bulbs, a practical advantage of the filaments is that the LEDs can be elevated for omnidirectional light, the same as an incandescent bulb.
And beyond their similarity to old-school filaments, it’s a novel and interesting packaging and mounting of LEDs. LED component packages are far from being cast-in-concrete; it’s still the wild west, and novel and interesting packaging may very well be the source for future growth.
Here are some of the LED-filament bulbs I saw at LightFair 2014 a few weeks ago:
Archipelago Lighting’s Thread candelabra lamp, as well as several other members of its Thread family, used the filaments:
…and a behemoth bulb, also from Archipelago Lighting:
Lighting Science Group had the retro-style filament lamps in A19 bulbs as well as candelabra-base.
Z-Light had a similar LED lamp, with the filaments arranged in a zig-zag pattern.
Z-Light is unique in that it’s the only vendor that also offers the filaments themselves: Here’s a link to a PDF of an LED filament spec sheet.
So how are LED filaments made? Here’s my understanding: The “filament” consists of relatively low-power LED chips (that is, unpackaged LED dice) mounted on a thin narrow glass (or transparent ceramic or sapphire) substrate. The LED chips are either joined by a metal trace, or jump-wire-bonded in series. Each end of the filament has a metal end for further assembly.
The filament is encapsulated in a resin made up of silicone and phosphor mixture that performs the usual transformation of the LED chips’ blue light into white. In addition, the filament can be ordered with some red LED chips to warm up the light spectrum.
With each filament capable of 1W, and assuming 20 LEDs/filament, it appears that the filament is a high-voltage, low current package. It also appears that the bulbs have an inert gas inside to help with the heat dissipation. The efficacy is as high as 130 lm/W at the filament level, but more like 100 lm/W at the bulb level. I’ve heard of pricing as low as $3 for a 6-filament bulb.
Typical dimensions are 38.5mm x 2.0mm
Here’s a link to a video of the filaments spot welded together prior to being placed inside the bulb. The whole process takes about a minute and a half.
A couple of stills of the welding process:
This (blurry) still from the video shows the filaments that are being spot welded together, prior to being placed inside of the retro-style LED bulb.
The operator rotates the tiny candelabra of filaments as she bonds each new filament to the group (below).
I have heard LED filament bulbs dismissed as a niche market of little interest to solid-state lighting folks. However, the bulbs themselves have a lot going for them in that they attention-getting, just as are filament-visible incandescents. The retro-style is one that consumers may be willing to pay more for as a high-end product. LED chandelier-style LED bulbs are currently kind of ugly. If you’re going to go with a flame-tip bulb, the filament style is pretty appealing.
But looking beyond retro-style bulbs, this is one of the first original, novel packaging concepts for LED that looks beyond point-source in a flat package.