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Comment by mwint | Hacker News Reader

Wait, hold on. I somewhat recently discovered I can “see” pulse-width modulation on dimmable LEDs by moving my eyes quickly over the LED and then examining the trail of dashes left by the light.

How does this square with vision being “paused” during the movement?

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Vision only seems to be paused briefly. If you repeatedly keep moving your eyes it seems to allow the blurriness through, there's probably a "timeout" mechanism. Probably better strategy to still see something in case your eyes are shaking for a long time for whatever reason than to not see anything

If you are following an object, the saccades routine itself is put on hold and you get more or less continuous eye motion, complete with smooth focus and field-of-view adjustments. I'm doing this for fun when walking alongside slow-rolling cars - the end result occasionally "looks like" a tracking shot straight out of a movie.

Edit: ...OK, field-of-view doesn't vary that much, unless you are Colonel Steve Austin with the telephoto augmentation.

Not following an object - this is the procedure:

1. Put LED at the bottom of vision 2. Look below LED, so now it’s at the top of vision 3. There’s a trail of light for a fraction of a second, seeming to start from the bottom of vision to the top.

I’m not smoothly tracking anything, just looking at one point and then another. I can clearly see the on-off duty cycles, and I’ve been playing with training myself to estimate frequencies with this method.

Hmm. I see something similar when looking quickly at or away from bright text (eg. end credits) on a DLP projector; it will get split into its constituent colors in the direction of my eye's movement. I guess the "double buffering" functionality does not completely shield one from experiencing the interim flashes.

That's what I do as well with tail lights of cars. There is a clear distinction between LED and normal lights: the LED's form a trail of dots.

I can see the color wheels of most projectors[1] by the colored light bleeding out through the ventilation on the side. I only notice it when I'm moving my gaze, stationary the light just blurs into a steady white.

[1] Except the pricier models, either with separate LCDs for three colors, or with very fast color wheels.

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