5 ms·

I've always been curious: does anyone else dart their eyes back and forth to determine if a light is blinking or not?I feel like it might be my superpower. I ca

I've always been curious: does anyone else dart their eyes back and forth to determine if a light is blinking or not?I feel like it might be my superpower. I can spot 60hz no problem. When I first saw the MacBook indicator, it was a lot of fun to finally see my talent put to use in an additional dimension. I remember seeing the modulation and thinking: oh cool, the entire duty cycle remains constant as they increase the on while decreasing the off.

trop 16y ago
From the patent ("Detailed Description of the Preferred Embodiments"): "The electrical pulses as shown in FIG. 3 have varied pulse widths because of the operation of PWM, and their actual pulse widths depend on the associated sinusoidal duty cycle function. The PWM frequency used in this embodiment is 125 Hz. In fact, preferred frequencies include any frequency sufficiently greater than that can be effectively distinguished by the human eye. However, power consideration for portable devices further prefer PWM frequencies to range within, for example, 100-200 Hz. ... It was determined through experiment that increasing the duty cycle according to a non-linear function gives the most pleasing visual effect while a simple linear ramp does not seem as natural."
- photon_off 16y ago
  This is consistent with what I claim. I never sad the apple indicator light was 60hz, I was just using that as an example as it's a very common frequency; I notice it especially with antennae, bridges, buildings, etc. Take a camera and set the shutter speed long enough so that you can blur the light, and you'll see the blinking effect that I do. The patent can claim it's not noticable, but it's pretty noticable to me. Interesting that they market even in their patents.
  - trop 16y ago
    Yes... Motion pictures, for example, are 24hz-30hz, which is just enough to get rid of noticeable flicker, but still risks strobing during fast camera movements.
    - photon_off 16y ago
      Another major factor in motion pictures is that each frame also contains a substancial amount of blur. This allows your mind to compensate for the lack of frames. I'm not sure how projectors work, exactly, but I suspect they also fade into and out of each frame in some way. That is, it probably doesn't operate like this: show frame -> clear screen -> show next frame. LEDs and the like are usually set up to be either on or off (a square wave) causing the flicker much more apparent. Street lamps are sort of a hybrid, they "flicker" at 60hz, but their flicker is not a square wave, but rather a sine wave.
aikinai 16y ago
I wouldn't really call it a superpower, I have it too and it's more of a curse. Also, the worst are cheap projectors that seem to alternate between red, green, and blue, so you see a rainbow every time you move your eyes between the projector image or your own notes. It's so frustrating to me, but no one ever believed me about it, so I guess not everyone has this curse.
- photon_off 16y ago
  Yep, exactly. Progressive scanning is pretty bad. I also find it distracting at night while driving as more and more cars' lights, especially tail, are pwm'd LEDs. High frequency, but still they flicker.
- sapphirecat 16y ago
  > cheap projectors that seem to alternate between red, green, and blue If you were curious, those would be single-chip DLP projectors: http://en.wikipedia.org/wiki/Digital_Light_Processing http://en.wikipedia.org/wiki/Digital_Light_Processing

trop 16y ago

From the patent ("Detailed Description of the Preferred Embodiments"): "The electrical pulses as shown in FIG. 3 have varied pulse widths because of the operation of PWM, and their actual pulse widths depend on the associated sinusoidal duty cycle function. The PWM frequency used in this embodiment is 125 Hz. In fact, preferred frequencies include any frequency sufficiently greater than that can be effectively distinguished by the human eye. However, power consideration for portable devices further prefer PWM frequencies to range within, for example, 100-200 Hz. ... It was determined through experiment that increasing the duty cycle according to a non-linear function gives the most pleasing visual effect while a simple linear ramp does not seem as natural."

photon_off 16y ago
This is consistent with what I claim. I never sad the apple indicator light was 60hz, I was just using that as an example as it's a very common frequency; I notice it especially with antennae, bridges, buildings, etc. Take a camera and set the shutter speed long enough so that you can blur the light, and you'll see the blinking effect that I do. The patent can claim it's not noticable, but it's pretty noticable to me. Interesting that they market even in their patents.
- trop 16y ago
  Yes... Motion pictures, for example, are 24hz-30hz, which is just enough to get rid of noticeable flicker, but still risks strobing during fast camera movements.
  - photon_off 16y ago
    Another major factor in motion pictures is that each frame also contains a substancial amount of blur. This allows your mind to compensate for the lack of frames. I'm not sure how projectors work, exactly, but I suspect they also fade into and out of each frame in some way. That is, it probably doesn't operate like this: show frame -> clear screen -> show next frame. LEDs and the like are usually set up to be either on or off (a square wave) causing the flicker much more apparent. Street lamps are sort of a hybrid, they "flicker" at 60hz, but their flicker is not a square wave, but rather a sine wave.

aikinai 16y ago

I wouldn't really call it a superpower, I have it too and it's more of a curse. Also, the worst are cheap projectors that seem to alternate between red, green, and blue, so you see a rainbow every time you move your eyes between the projector image or your own notes. It's so frustrating to me, but no one ever believed me about it, so I guess not everyone has this curse.

photon_off 16y ago
Yep, exactly. Progressive scanning is pretty bad. I also find it distracting at night while driving as more and more cars' lights, especially tail, are pwm'd LEDs. High frequency, but still they flicker.
sapphirecat 16y ago
> cheap projectors that seem to alternate between red, green, and blue If you were curious, those would be single-chip DLP projectors: http://en.wikipedia.org/wiki/Digital_Light_Processing http://en.wikipedia.org/wiki/Digital_Light_Processing