[FriedPickles]

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

[jessriedel]

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/Planckia...

[mensetmanusman]

The human eye will see white when a pixel flashes through all of the colors quickly in time.

[mark-r]

You don't need all the colors. As every household white LED bulb proves, you can get it with just a combination of blue and yellow.

[rini17]

You'll get atrocious CRI/sick skin tones that way. There's much more fleshed out spectrum in nowadays LEDs, especially warm white variants.

[ajuc]

But that means it has reduced refresh rate.

[wmertens]

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

[Etherlord87]

How quickly? Surely well above 1 kHz (1000 FPS). Otherwise you will see flickering.

[mastax]

Single chip DLP projectors strobe red, green, blue, white sequentially. Modern DLPs use separate light sources (LED/Laser) and pulse them at a high frequency - kilohertz I assume. Before we had high-power LEDs DLP projectors used a xenon lamp and a color wheel (https://www.projectorjunkies.com/color-wheel-dlp/) spinning at as little as 60 revolutions per second. This caused a "rainbow effect" which was very annoying to some people, but apparently enough people didn't notice it that those products got sold anyway. So somewhere around 180Hz is the bare minimum.

[jessriedel]

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

[PaulHoule]

See also 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-o...

Here is a video of people doing it

https://www.youtube.com/watch?v=5PquJdIK_z8

[duskwuff]

> 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/003189...

*: With the exception of phosphor-converted LEDs, which are uncommon.

[exmadscientist]

> 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!