I found a bunch of axial red LEDs that have something black inside them. They work fine, they are not burned.

Black inside LED

I also have some yellow ones with the same black material, for which I was lucky enough to have a datasheet.

yellow leds with black material

Not all type of LEDs have this black material inside them. What is this, and what difference does it make to the LED's specifications?

  • \$\begingroup\$ Anything not red inside red transparent plastic will look black. \$\endgroup\$
    – Andy aka
    Sep 1, 2021 at 11:30
  • 5
    \$\begingroup\$ Do the red LEDs also blink? \$\endgroup\$
    – JRE
    Sep 1, 2021 at 11:33
  • \$\begingroup\$ @JRE yes they both do \$\endgroup\$ Sep 1, 2021 at 11:37

1 Answer 1


Ok I think it was silly to ask, The datasheet of the yellow LED says "with build-in IC for blinking" So this is it!

blinking led

  • 1
    \$\begingroup\$ Look inside an RGB colors-changing LED to see its black tiny little IC. \$\endgroup\$
    – Audioguru
    Sep 1, 2021 at 15:30

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