Light enigma

[DivideByZero]

If light were to blink on and off and the speed of light continuously, would the light appear to be on or off?

[npts2020]

Well, the flourescent lights at your school blink on and off 60 times every second, do they appear to be on or off?

[GDG]

What exactly do you mean by blinking "at the speed of light"? The speed (aka velocity) doesn't translate well into frequency, when light can have a wide variety of frequencies and wavelengths.

 

At high blinking frequencies, you would see a continuous light. This is why you don't notice that TV screens and computer monitors are refreshing constantly. IIRC, > 80Hz looks like continuous illumination. As you slow the blinking frequency down, the light would begin to strobe, and finally you'd just see discrete "on" and "off".

[swansont]

If light were to blink on and off and the speed of light

 

As GDG has noted, this is is ill-defined.

 

(The strobing would also be continually, rather than continuously)

 

Are you asking about persistence of vision, or inquiring about some other possible effect?

[DivideByZero]

I guess what I'm talking about is that it blinks on and off as fast as theoretically possible. Maybe on then off then on at Planck's time constant (smallest unit of time).

 

If the light was on and suddenly, within the smallest unit of time, it blinks off then on again, we wouldn't notice it.

 

And same thing the other way.

If the light was off and suddenly, within the smallest unit of time, it blinks on then off again, we wouldn't notice it.

 

So what happens if it blinks on and off repetitively as fast as possible?

[GDG]

Basically, you won't be able to detect any variation in intensity that oscillates faster than around 80 Hz (probably a bit less, actually). You would see it as unvarying.

[swansont]

If you were able to engineer electronics to turn it on and off that fast, you might be able to engineer a detector that has that response bandwidth. If you modulate a signal at f, you will get a response at f on your detector, so your detector has to be capable of responding to that modulation.

[npts2020]

You can build a device to measure events down to the nano-second (maybe even pico-second by now) range. Your eyes would notice no period of time when there wasn't light at that speed of flashing. After about 8-10 cycles per second, afterimages remain in your eyes longer than the light is off. As I stated above, flourescent lights turn on and off 60 times a second (50 for those on 50Hz grids). By the time you have gotten to this relatively slow on/off speed your eyes will not notice any increase in the frequency.

[Klaynos]

I use an ultrafast laser, we measure light pulses that are 100fs...

[npts2020]

I use an ultrafast laser, we measure light pulses that are 100fs...

 

Thanks for the clarification Klaynos. That's what I get for depending on memory and not looking it up. Now that I have looked, it seems as if the shortest lightpulse is under a femtosecond, aiming for around 600 attoseconds. I have a related question that may be better answered in the biology forum, is there any shortest pulse of light that is required to be visible to the human eye or will any visible light be detected?

[iNow]

This study suggests a minimum of 20 - 30 milliseconds. The term used for this type of research is "temporal hyperacuity" or "temporal resolution limit."

 

 

http://dx.doi.org/10.1016/S0042-6989(02)00301-2

The spatial grain of the human visual system has always been a central topic for visual sciences, and the optical and physiological basis of perceptual limitations are well described. In particular, we have thorough accounts of spatial hyperacuity, which refers to a precision in the spatial localisation of stimulus contours that is better than the photoreceptor grain that determines spatial resolution. However, although the temporal resolution of the human visual system is comparably well described, we have almost no direct knowledge about the precision of localising visual stimuli in time in the absence of correlated spatial cues.

 

The present study addresses this question by comparing directly the temporal resolution of human observers with their temporal acuity as measured in a temporal bisection task. Despite some improvement with practice,

temporal acuity in this task does not fall below 20–30 ms in the best case

, which is similar to the temporal resolution limit, and performance does not improve for comparison tasks with multiple stimulus presentations.

 

The absence of visual hyperacuity for purely temporal modulations as tested here contrasts with processing limitations for other types of visual information in comparable tasks, and with other sensory modalities, in particular to those of the auditory system. Such differences can be interpreted in the context of the ecological requirements for organising behaviour, and the functional design of nervous systems.

[Klaynos]

Thanks for the clarification Klaynos. That's what I get for depending on memory and not looking it up. Now that I have looked, it seems as if the shortest lightpulse is under a femtosecond, aiming for around 600 attoseconds. I have a related question that may be better answered in the biology forum, is there any shortest pulse of light that is required to be visible to the human eye or will any visible light be detected?

 

We can make single photon emitters, and there is some evidence that the human eye can detect a single photon.

[Xittenn]

Attophysics Atomic Photography

 

http://www.nature.com/nature/journal/v419/n6909/full/419789a.html

 

Electron Stroboscope

 

http://focus.aps.org/story/v21/st7

 

http://www.sciencedaily.com/releases/2008/02/080222095358.htm

 

~

[npts2020]

Thanks for the info one and all. The single google search I did was not very successful but you guys have managed to give me enough to think about.