5 ms·

It can produce all the colors of the rainbow. But no magenta. Perhaps they can quickly pulse the LED enough between multiple wavelengths.

PaulHoule 2y ago
See also https://en.wikipedia.org/wiki/Spectral_color https://en.wikipedia.org/wiki/Spectral_color This reminds me of the observation I had in high school that I could immerse LEDs in liquid nitrogen and run them at higher than usual voltage and watch the color change. I got a PhD in condensed matter physics later on but never got a really good understanding of the phenomenon but I think it has something to do with https://www.digikey.com/en/articles/identifying-the-causes-of-led-efficiency-droop https://www.digikey.com/en/articles/identifying-the-causes-o... Here is a video of people doing it https://www.youtube.com/watch?v=5PquJdIK_z8 https://www.youtube.com/watch?v=5PquJdIK_z8
- duskwuff 2y ago
  > I got a PhD in condensed matter physics later on but never got a really good understanding of the phenomenon but I think it has something to do with The color of most* LEDs is controlled by the band gap of the semiconductor they're using. Reducing the temperature of the material widens the band gap, so the forward voltage of the diode increases and the wavelength of the emitted light gets shorter https://www.sciencedirect.com/science/article/abs/pii/0031891467900626 https://www.sciencedirect.com/science/article/abs/pii/003189... *: With the exception of phosphor-converted LEDs, which are uncommon.
  - exmadscientist 2y ago
    > phosphor-converted LEDs, which are uncommon No, they're extremely common. Every white LED in the market is phosphor-converted: they're blue LEDs, usually ~450nm royal blue, with yellow-emitting phosphors on top. Different phosphors and concentrations give different color temperatures for the final LED, from about 7500K through 2000K. (Last I looked, anything below about 2000K didn't look right at all, no matter what its manufacturer claimed.) Bigger LEDs are often phosphor-converted as well. Most industrial grow lamps use this type of LED. So they're around! You're probably looking at some right now!
jessriedel 2y ago
It also can't produce white or anything else in the interior of this diagram (as well as, as you mention, shades of magenta and purple that lie on the flat lower edge): https://upload.wikimedia.org/wikipedia/commons/b/ba/PlanckianLocus.png https://upload.wikimedia.org/wikipedia/commons/b/ba/Planckia...
- mensetmanusman 2y ago
  The human eye will see white when a pixel flashes through all of the colors quickly in time.
  - ajuc 2y ago
    But that means it has reduced refresh rate.
    - wmertens 2y ago
      The two are not related at all. Refresh rate is how fast it can accept input, whereas this is how fast it can do TDM of colors and intensities
      - deleted 2y ago
        [deleted]
  - Etherlord87 2y ago
    How quickly? Surely well above 1 kHz (1000 FPS). Otherwise you will see flickering.
    - jessriedel 2y ago
      According to this, humans can't see flicker above 100 Hz for most smooth images, but if the image has high frequency spatial edges then they can see flicker up to 500-1000 Hz. It has to do with saccades. https://www.nature.com/articles/srep07861 https://www.nature.com/articles/srep07861

PaulHoule 2y ago

See also https://en.wikipedia.org/wiki/Spectral_color https://en.wikipedia.org/wiki/Spectral_color This reminds me of the observation I had in high school that I could immerse LEDs in liquid nitrogen and run them at higher than usual voltage and watch the color change. I got a PhD in condensed matter physics later on but never got a really good understanding of the phenomenon but I think it has something to do with https://www.digikey.com/en/articles/identifying-the-causes-of-led-efficiency-droop https://www.digikey.com/en/articles/identifying-the-causes-o... Here is a video of people doing it https://www.youtube.com/watch?v=5PquJdIK_z8 https://www.youtube.com/watch?v=5PquJdIK_z8

duskwuff 2y ago
> I got a PhD in condensed matter physics later on but never got a really good understanding of the phenomenon but I think it has something to do with The color of most* LEDs is controlled by the band gap of the semiconductor they're using. Reducing the temperature of the material widens the band gap, so the forward voltage of the diode increases and the wavelength of the emitted light gets shorter https://www.sciencedirect.com/science/article/abs/pii/0031891467900626 https://www.sciencedirect.com/science/article/abs/pii/003189... *: With the exception of phosphor-converted LEDs, which are uncommon.
- exmadscientist 2y ago
  > phosphor-converted LEDs, which are uncommon No, they're extremely common. Every white LED in the market is phosphor-converted: they're blue LEDs, usually ~450nm royal blue, with yellow-emitting phosphors on top. Different phosphors and concentrations give different color temperatures for the final LED, from about 7500K through 2000K. (Last I looked, anything below about 2000K didn't look right at all, no matter what its manufacturer claimed.) Bigger LEDs are often phosphor-converted as well. Most industrial grow lamps use this type of LED. So they're around! You're probably looking at some right now!

jessriedel 2y ago

It also can't produce white or anything else in the interior of this diagram (as well as, as you mention, shades of magenta and purple that lie on the flat lower edge): https://upload.wikimedia.org/wikipedia/commons/b/ba/PlanckianLocus.png https://upload.wikimedia.org/wikipedia/commons/b/ba/Planckia...

mensetmanusman 2y ago
The human eye will see white when a pixel flashes through all of the colors quickly in time.
- ajuc 2y ago
  But that means it has reduced refresh rate.
  - wmertens 2y ago
    The two are not related at all. Refresh rate is how fast it can accept input, whereas this is how fast it can do TDM of colors and intensities
    - deleted 2y ago
      [deleted]
- Etherlord87 2y ago
  How quickly? Surely well above 1 kHz (1000 FPS). Otherwise you will see flickering.
  - jessriedel 2y ago
    According to this, humans can't see flicker above 100 Hz for most smooth images, but if the image has high frequency spatial edges then they can see flicker up to 500-1000 Hz. It has to do with saccades. https://www.nature.com/articles/srep07861 https://www.nature.com/articles/srep07861