| So far the efficient LEDs require a monocrystal semiconductors, with the functional structure built into it. That means you get light emitting cubes that need to be connected at exact points designed for it. So you can not just tuck a bit of "sand" into some tube or around a wire and expect it to work.
In theory it would be possible to make the LED dies in the form of long stripes, even with many individual diodes in series, but that arrangement would lead to impractically high power density (the problem being the cooling of such thing), so it is used only on some specialized application (medium density pixel car headlights, where the LED group is closely connected to the control IC), but not for general lighting.
Plus there is yet another aspect that makes virtually any large size die impractical: Each semiconductor process has certain number of defects per unit area. Manufacturing without such defects is not physically possible, the only thing you may do is either live with certain scrap rate or design the product so you can isolate the defective part by e.g. configuration (used on large chip processors, memories or so). Now when such defect happens to be on an active part, it renders it not functional. As LEDs are just simple diodes, there is no way to isolate any defective part of it, it would mean the whole die would become unusable.
Now if you design your chips small enough, those defects will affect only some and majority will be OK. But once you attempt to make the dies larger, the laws of statistics make sure you have to scrap way bigger percentage of your production, so have lower yield, so higher cost per good unit.
So obviously smaller, lower power units means less waste.
If you go too far to too small dies, the handling and cutting the higher number of them for the given total power, which also means extra cost.
So there is an optimum and for common LEDs that seems to be around 200..500um side squares rated for about 15..20mA so 40..60mW per die for gas cooled filaments or about 300mW 100mA units for COB LEDs use.
You may make an amorphous LED on a narrow stripe of glass or so also with a reasonable power density, but amo-LEDs do not reach usable efficacy and/or lifetime, at least not yet.
So you get stuck with roughly 50mW chips (roughly 200um side size each), which you need to spread about 20 of them along 2..3cm stripe support (to allow tge heat to get dissipated to the cooling gas; so about 1..1.5mm spaced) to form the 1W "filament". Larger chips are made only for the precission beam control optics (auto headlights, torches, flashlight,...), but where the higher cost per watt or lower lifetime associated with higher power density gets justified (a flashlight is very unlikely to make more than couple 100's hours till it disintegrates by itself after two decades of use, while street or office light will make 20k hours within two years).
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