# Thread: What did I just see?

1. I was playing my acustic guitar and i noticed that when i played a B note on the A string that I could see violet and green light coming off of the string while it vibrated. I have copper strings (I think) and i was under florelecent light. Do you know what caused this?

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3. B2 note is approx. 123 Hz. If you're in the US electricty supply is 60 Hz. and I think fluorescent lights flicker at that frequency. Your guitar only needs to be slightly out of tune to get some sort of interference between the vibrating string and light reflecting off the soundboard. Just a guesspothesis.

If you're in the 50 Hz. UK as your name suggests then you're badly out of tune, or more likely my guess is crap.

4. Originally Posted by BunBury
If you're in the US electricty supply is 60 Hz. and I think fluorescent lights flicker at that frequency.
Actually all ac lamps flicker at twice the supply frequency. That's because the brightness reaches peak at both positive and negative halves of the cycle.

5. Can anyone else see it? If not, the likely explanation is a perceptual one.

6. Originally Posted by Osby
Originally Posted by BunBury
If you're in the US electricty supply is 60 Hz. and I think fluorescent lights flicker at that frequency.
Actually all ac lamps flicker at twice the supply frequency. That's because the brightness reaches peak at both positive and negative halves of the cycle.
That would explain a mild stroboscopic effect. But the violet and green light is a bit of a puzzle.

7. This reminds me of a curious string of LED Christmas lights I've seen, that might provide a clue. Each plastic bulb contains a red LED and a green LED. The maker wanted the colour to fade between red and green, and accomplished this by flickering the LEDs at higher frequency than human eye 24Hz. If you stare at the lights they do have this smooth transition effect. However, if you quickly glance over them, you see one bold colour - either solid red or green. The lights play crazy colour-strobing feedback tricks if you let your gaze roam naturally.

Perhaps there were two different lighting conditions on the guitar string, that appeared violet or green in relation to each other?

EDIT: BTW I got a number of people to confirm this, and some noticed it instantly, while others just couldn't no matter how they blinked and glanced.

8. Sorry I can't help with the OP's question, aside from synesthesia. But the flashing LED thing is probably due to scanning the eye quickly and seeing the flashes on slightly different parts of your retina.

The Exploratorium in San Francisco has (used to?) an LED bar that sequences images or text at a very high rate such that you could sweep your eyes across it and see the image spread out across the wall. It was an Artist in Residence piece and may have been commercialized someplace. I could never get it to work because I kept fixating on the bar no matter how I tried to "just sweep"...

9. Originally Posted by DrRocket
That would explain a mild stroboscopic effect. But the violet and green light is a bit of a puzzle.
Perhaps the flickering of the lamp went though phases of different colour, invisible to the human eye because of its inertia, but brought out by the stroboscopic effect.

Just a thought...

10. Actually all ac lamps flicker at twice the supply frequency. That's because the brightness reaches peak at both positive and negative halves of the cycle.
Different colours for the two sides of the phase ?

Try lay the guitar flat on a table It might disappear.
Putting all the lights out you also won,t see it if the light" is more like a - local at the snares - colouring of the usual light in the room.

11. Originally Posted by Leszek Luchowski
Originally Posted by DrRocket
That would explain a mild stroboscopic effect. But the violet and green light is a bit of a puzzle.
Perhaps the flickering of the lamp went though phases of different colour, invisible to the human eye because of its inertia, but brought out by the stroboscopic effect.

Just a thought...
I thought about that, but I don't think there would be enough color variation over an electrical cycle. If that were the case then ambient light photography under incandescent or flourescent lights ought to show some pretty weird color effects that don't show up.

12. *Our speculations in gadget form: http://hackaday.com/2009/11/23/elect...rings-for-you/

I'm guessing that for LimeyBrain only one strobe (fluorescent) was present; the other colour light was from continuous natural or incandescent. The lights appeared relatively violet or green in contrast, because prior to illuminating the strings they had bounced off different surfaces.

13. Originally Posted by Ghrasp
Originally Posted by Osby
Actually all ac lamps flicker at twice the supply frequency. That's because the brightness reaches peak at both positive and negative halves of the cycle.
Different colours for the two sides of the phase ?
No. The color should be the same for both halves of the cycle.

Here's another possibility: http://en.wikipedia.org/wiki/Fechner_color

14. Originally Posted by Osby
Originally Posted by Ghrasp
Originally Posted by Osby
Actually all ac lamps flicker at twice the supply frequency. That's because the brightness reaches peak at both positive and negative halves of the cycle.
Different colours for the two sides of the phase ?
No. The color should be the same for both halves of the cycle.

Here's another possibility: http://en.wikipedia.org/wiki/Fechner_color
That strikes me as the most plausible explanation so far.

15. I think it is to coincidental that it happens near the frecquency of the electricity to not be related with that (allthough coincidences happen).

What I,m thinking of is that as the phase is 220 to the ground the ground is also 220 to the phase (relative). We don,t experience it that because as we stand fysically on the ground in our "frame of reference" the earth is at zero voltage to us and the phase fluctuates but it is relative.

The snare therefor also has a fluctuating voltage (electric potentialdifference) to the phase of the electricitysystem.
If this relation fits putting out the light (striking the snare in the dark) would stop the luminescense of the air. Another way to test a relation to the electricity frecquentie would be by wearing nike,s in stead of playing guitar on socks (or barefoot). Or putting the guitar on a generator without a phase and earth wire.

16. Originally Posted by Ghrasp
I think it is to coincidental that it happens near the frecquency of the electricity to not be related with that (allthough coincidences happen).

What I,m thinking of is that as the phase is 220 to the ground the ground is also 220 to the phase (relative). We don,t experience it that because as we stand fysically on the ground in our "frame of reference" the earth is at zero voltage to us and the phase fluctuates but it is relative.

The snare therefor also has a fluctuating voltage (electric potentialdifference) to the phase of the electricitysystem.
If this relation fits putting out the light (striking the snare in the dark) would stop the luminescense of the air. Another way to test a relation to the electricity frecquentie would be by wearing nike,s in stead of playing guitar on socks (or barefoot). Or putting the guitar on a generator without a phase and earth wire.
And this is the most ridiculous attempt at an explanation so far.

17. Sorry for misreading but even when it is an accoustic guitar in the whole setup and electric / magnetic fields generated to create the light in which the snare is seen (and the eye functions) the snare has a fluctuating potential to the source of the light, the fase.
The snare being on a fluctuating potential when it fluctuates itself in a resonating way to the electric fluctuating field it is a part of it becomes active in that field in two directions (snare moves the copper up and down with quick accelerarions) and influences the light locally in two ways one violet the other green two colours that oppose each other in the spectrum of colours as the movement of the copper is opposing direction also.

Call it ridiculous but at least it can be prooven to be ridiculous (or not).
So "Limeybrain" do mr Rocket a favour ... proof it ridiculous (if you have the opportunity).

Fechner color is not well understood at all so for sure it doesn,t explain much.

18. Hi....

Copper strings? I knew guitar strings could be either nylon or metal but i did not realise they'd be copper?

Erm....bit of a mystery although.....

If you get a white spinning top with wholes in it and spin it really fast the wagon wheel effect........you will see green / red sort of alternating pattern; I suspect that this was the same when you plucked your string.

Other theory is that the string is somehow magnetised in one direction and you plucking the string released photons...but to be honest, i dont think the string would be able to vibrate at the necessary frequency needed for photon released due to magnetic oscillations.

19. The four lower strings including the A string usually comprise a stainless steel core with a helical winding of a copper alloy - bronze or brass. The steel provides tensile strength and the copper alloy provides mass.

20. I would want to know if this only happens with electric light or also with sunlight. If it doesn,t work with sunlight it is more likeley that the frecquency correspondance of the note with the electric frecquency is a factor.

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