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This light bulb is classified by its manufacturer in Europe as a Classic A 7W 230V 2700K 806lm B22d bulb. To me this bulb has the appearance of an incandescent light bulb with thin filaments of yellow/orange conducting material which give off the glow. I thought an LED was a surface mounted device (SMD) on a PCB. Can someone please explain what allows this type of bulb to have an LED classification? Are the LEDs located somewhere on the conducting material? enter image description here

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    \$\begingroup\$ It's a variation of Chip-On-Board (COB) simply called filament LEDs. Bigclivedotcom has several videos about them: youtu.be/hFtfMtFSD8A \$\endgroup\$
    – winny
    Jun 8, 2023 at 12:53
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    \$\begingroup\$ @winny That is a nice video. I don't know if this is why you chose it, but at 8:30 he shows a picture he took of the filaments at low current/dim brightness. In this picture you can easily count the 18 individual LEDs hiding under the phosphor, which illustrates the construction nicely. \$\endgroup\$
    – Frodyne
    Jun 9, 2023 at 7:03
  • \$\begingroup\$ Those "LED Filament" light bulbs are intentionally made to look like an (older, low power, "vintage") incandescent bulbs. Newer incandescent lightbulbs (esp. when powered off) look somewhat different. \$\endgroup\$
    – fraxinus
    Jun 9, 2023 at 9:40
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    \$\begingroup\$ Just to add to the existing and accepted answer, COB LEDs were actually a very welcome new technology because this is what finally made it possible to have practically any shape of LED light with homogenous light output. For more light, you simply use a larger area but still get the same benefits. The automotive industry, among others, just couldn't wait to finally lay hands on a LED that can be shaped at will and will no longer emit a clearly visible string of small points. \$\endgroup\$
    – Gábor
    Jun 10, 2023 at 9:40

3 Answers 3

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The LEDs are hiding in the filaments.

Surface mount LEDs can now be made very small. Each filament in this style of lamp has a long string of surface mount blue or violet LEDs wired in series. The entire filament is then coated in yellow phosphor, so that it glows with (something approximating to) white light.

The total number of LEDs wired in series is chosen to match the expected supply voltage (120V or 230V, typically). The manufacturer may wire the filaments in series or parallel, as required.

The AC-to-DC conversion is done in the base of the lamp.

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    \$\begingroup\$ Re, "Surface mount LEDs..." Has anybody ever decapped one of those "filaments?" Usually, when we say, "surface mount," we are talking about components that are packaged to be mounted on the surface of a circuit board. But obviously, those "filaments" are too skinny to contain any such thing. I wonder if what's embedded in those skinny yellow plastic things isn't just naked LED chips connected to each other by bonding wires. \$\endgroup\$ Jun 8, 2023 at 21:51
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    \$\begingroup\$ P.S., LEDs always have been "made very small." Even in those classic, 5mm, thru-hole packages, the actual LED chips were tiny. \$\endgroup\$ Jun 8, 2023 at 21:52
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    \$\begingroup\$ @SolomonSlow Not decap as such, but hackaday.com/2023/02/18/… (linking to a Youtube video) shows some of the "filaments" repurposed after being removed from the transparent envelope. \$\endgroup\$ Jun 9, 2023 at 15:21
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This is how a typical LED filament looks like when magnified and somewhat simplified:

enter image description here

Image credit

It is still "Chip-on-board" (COB), the difference is that the "board" is made as thin as practical

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  • \$\begingroup\$ Just watched Big Clive's Dubai Lamp videos, and he said that the filament construction is flip-chip, so for what he sees, there are no bond wires between the chips. And this makes sense because it improves reliability (I believe). In the link you provided, I found this confirmed -- that the flip-chip kind is more reliable. \$\endgroup\$ Nov 28, 2023 at 1:42
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Just like the LED devices you know are a semiconductor device (the actual light-emitting diode) embedded in a light-conducting plastic:

The LED devices actually are the yellow elements. They are a series of the actual diodes, usually on a transparent substrate, with traces to connect them that are thin enough to not be obvious to the eye.

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