Power supply to sodium street lamps

[Calvesy]

While rolling my eyeballs around one night I noticed that the blurred trails of sodium street lamps left about 100 long dashes per second on my retina, as you might expect from 50Hz ac.

However, between the dashes was not a brief period of darkness, but a small dot, Like ______.______.______.______.______.______.______

I've seen this phenomenon while abroad, and over many weeks here, so it's not a temporary or local anomaly.

Anyone know where the dot gets its power from?

[jake-the-peg]

Are you suggesting that you can differentiate between a hundredth of a second and a fiftieth of a second by eye and then resolve a fraction of that?

Or have I misunderstood? 

[Calvesy]

It's not about me, you could try this at home, observe the phenomenon, and come back to me. It helps if the lamp is some distance away otherwise it's width spans the gap when the current changes direction. If you can't roll your eyeballs try vigorously shaking binoculars.

You can also see how the beam scans a TV screen, or see the segments of a LED display lit up one at a time as number characters are built. Also useful for counting helicopter rotors during flight. Enjoy!

[JOEYSHABADO]

Your eyes do not send a perfect signal of events to your consciousness, it is not like a 'seamless buffer'. It is object-oriented, and not event oriented. (Try googling for Rensink+klin+visual world). There is not way you could rely on your visual perception as a reflection of sinusoidal light emittance.

[Tim Baxter]

I agree that any pulse light emitter such as discharge (sodium) and LED's will seem to cause broken but regular lines in your vision when your eyes 'scan' across them.  It's simply 'retention of vision' or 'persistance' of your light sensitive cells which give you the trail of lines across your scanning horizon.  However, the dots are a little more problematic to explain, if they ever appear like ...---... send help immediatley!

[Calvesy]

Aristotle claimed that men had more teeth than women. He was married twice and didn't think of looking at either of his wives' mouths. Thank you to those who understand that science comes from empirical evidence. Anyone can see this phenomenon, I hope you have a look and wonder as I have. An answer without ridicule would be nice.

[jake-the-peg]

And Percival Lowell thought there were Martians because he thought he could see canals and didn't question his observations too deeply.

Your question was where the dot got it's power from implying that the effect is real and not an artifact of your vision - I think most people are just questioning your experimental method and how you had discounted artifacts in the eye before drawing the conclusion that the effect was real.

Maybe a photo with a moving camera?

I don't think Tim's morse code gag quite crosses into ridicule.

[Calvesy]

It's OK I've found out the answer: In AC voltage and current are slightly out of phase. This means that they are not zero at the same instant. Power is the product of voltage and current, so when the voltage changes polarity, there is a slight lag before the current alternates, causing the lamp to light in this brief instant.

I would still invite anyone interested to roll your eyeballs around and observe the trails of a distant street lamp at night.

Budget: �0.00 , Duration of experiment: 1 second

[Tim Baxter]

- .... .- -. -.- ...     .--- .- -.- .

[Calvesy]

Thanks, Jake?

I've taken a picture of a distant street lamp through a telephoto lens on my SLR and smacked the camera as I pushed the button. If the picture comes out I'll upload it somewhere just to prove I'm not mad. Like a sane person would be on this site anyway!