Dimming led's ?

LED brightness is usually PWM. I suspect that circle case is PWM on all the LEDs with some software doing the patterns. Leds can be wired in a matrix to reduce the number of drivers.

That TI capacitive touch thing is cute, but conductive plastic resistive touch sensing would be easier.

Digital outputs are one or zero but can be flash LEDs very quickly, faster than your eye can see. The eye does perceive the integral of the flashing, so the duty cycle can be varied to adjust the brightness. That's all.

An issue with this is if the flashing is not fast enough, you won't see anything while the LED is stationary, but in motion you can see multiple images as it flashes on and off. They take advantage of this in toy wands that can spell out a message as you wave the wand in the air and the multiple LEDs are flashed on at the appropriate times to show letters and words. It's like the opposite of the moving message displays. The wand moves and the message stays still. Car tail lights can create multiple images as you turn your head making it look like there are many cars when there is only one or two.

An easy way to do it, is with a transistor having a capacitor from collector to base; the base resistor and that capacitor (Miller capacitor) make a slow-slewing output voltage. It also buffers a logic output (sub-milliamp) up to full LED drive (if you really want that, nowadays; thirty years ago, you definitely did).

I dislike the PWM-direct approach, because it requires logic, and because it generates EMI, and causes light output artifacts. Muxed LED displays, ditto.

Let's avoid that.

The logic is available already built-in to almost every MCU

So use a series inductor

CH

If you scan an LED matrix at 1 KHz, the AM band is the 1000th harmonic.

I suspect that the trailing LEDs are dimmed by a programmed PWM with a decreasing duty cycle based on their distance or time since the corresponding point has been touched.

It might be simply down to the use of phosphor coated LEDs (white LEDs) producing an afterglow effect - just a thought. However, I'd have expected the blue component to die off immediately leaving a green/blue afterglow which I didn't observe on closer inspection of that video. However, I also can't detect such a green/blue afterglow shift whenever I switch GLS LED lamps off either so who knows?

Johnny B Good wrote: ===================

** Think again...

White LEDs do not use phosphors.

The process is quite different and is called " scintillation" . No afterglow at all.

...... Phil

I guess the people who make LEDs don't know they are doing it wrong.

There are more than one way to skin a cat. White light can be produced from LEDs by using RGB LEDs in varying combinations to produce different intensities of light. The other common way is to use a blue LED with yellow phosphors or other combinations of phosphors to get better CRI.

There is apparently some persistence in the ~460nm Blue-excited YAG:Ce3+ yellow phosphors typically used but it's fairly **brief** (double digit nanoseconds).

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** Yaawnnnnnn - go f*ck a dead donkey. ** So not "white LEDs" at all !!!!!!!!!!!!!!!!!!! Fuckhead.

...... Phil

I have a small screw in three LED white night light that when I turn it off it continues to glow for a number of seconds.

Looks like some sort of phosphor to me.

Most LEDs that are white are now using red/green/blue LEDs - I know, my store sells them all the time)...

John :-#)#

Scintillators often do produce some after-glow - the states excited don't emit visible light immediately - but decay time constant can be a short as a nanosecond or so, at least for most of them.Low level impurities can throw in the odd site that decays more slowly.

Anything rather than read a textbook.

A proper "white" LED would produce a continuous spectrum that looked as it f it came from a hot thermal radiator like the sun.

Happily the human eye has only three colour sensors - red, green and blue - so you can fool it with a mix of three narrow band emitters that you can get as three different-coloured LEDs.

You can also fool it by embedding a blue LED in phosphor loaded plastic where some of the the blue light emitter by the LED is absorbed by the phosphor and re-emitted at longer wavelengths to fill in enough of the longer wavelengths to satisfy the human eye. These are sold as "white" LEDs.

"Scintillation" is usually reserved for cases where the phosphors are excited by higher energy particles like electrons, helium nuclei or X-ray photons.

It's still fluorescence. If you want to get technical "phosphorescence", should be reserved for cases when energy level excited in the emitter is a triplet state, which is likely to decay more slowly than the usual singlet state, but only photochemists seem to care. Or at least they did when I was a postdoc (1971-73).

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** ROTFL !!!! ** Might it be a electro cap discharging ?? ** Then they are NOT "white LEDs" !!!!!!!!

White LED lighting is everywhere now, using high efficiency blue /violet LEDs with a yellow coating that turns the light white.

Google it if you are really so far out of touch.

...... Phil

Bill Slowman is a Fucking IDIOT & total prick

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** Is it visible to the human eye ???

No.

** Massively irrelevant, pedantic CRAPOLOGY !!

** Yawnnnn......

..... Phil

That's one way of looking for after after-glow. It only detects remarkably long-lived after-glow, but Phil is happy to exclude any other detector.

Not something that Phil wants to know, in other words.

Something else that Phil doesn't feel any need to know about either. He does like to protect his ignorance, and he has been remarkably successful.

It's not a "yellow coating" so much as a yellow phosphor which absorbs some of the blue light and re-emits it at longer wavelengths, which doesn't actually produce light that is all that white.

The spectrum doesn't look much like the solar spectrum, and the colour rendering isn't wonderful, but since Phil clearly hasn't taken his own advice, he doesn't seem to know about that.