Looking at a Filament LED

[harerod]

 I am a big fan of those "filament" LED-bulbs for E27 sockets. I had a defective one lying around in the office for a while. Today I finally cracked it open and had a closer look at the "filaments". These consist of 28 LED's on ceramic substrate, coated with a luminescent layer that shifts short wave light to longer wavelengths. 

For initial tests I illuminated the filaments by near-UV light, which looked really cool.

Then I tried to light the LED's themselves. This barely worked, since the highest voltage readily available at my desk is 70Vdc. At that voltage the LED's barely lit up, drawing a current below 0mA. 

The spectrum for the single filament shows the peak for the blue pump light at about the same height as the red light. However, under nominal operating conditions the blue peak would be much less prominent.

So, what do we do with this kind of information? First obvious choice would be to furnish a Darth Vader figure with a cool light sword.

Or, with Hanukkah around the corner, this may serve as an inspiration for Dad/Son projects to bring some light into your home.   

Take care with the voltage, though - unless you opt for external UV illumination.

Edit: Added UV pump spectrum.

[Gyro]

You might want to check out some of Big Clive's videos, he's done quite a few on LED filaments... https://www.youtube.com/@bigclivedotcom/search?query=LED filament

[tooki]

You can get them in all kinds of variants on Aliexpress. I used 3V, 38mm ones to make a giant-digit thermometer. Using the low-voltage variants makes it way easier and way safer to drive them.