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| Human Eye -- Peak or Average Response |
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| tooki:
--- Quote from: Nusa on June 10, 2019, 01:18:55 am ---24 Hz may give you persistence of vision, but flicker is easy perceived by just about everyone. Still, even that was pretty amazing to people early on in the moving pictures industry. These days it's upsampled for display, unless you want the old-time effect on purpose. --- End quote --- The 24fps film “look” is from being able to use shutter speeds as slow as 1/24 sec, allowing a small amount of motion blur. But indeed, 24fps is flickery, which is why cinema film projectors actually project each frame twice or three times before advancing the film, producing an effective “display” frame rate of 48 or 72fps. (Digital cinema projectors use higher frame rates still, AFAIK.) --- Quote from: Berni on June 10, 2019, 05:47:20 am ---At a low frequency of 24 Hz the only thing that will be significantly noticeable is that everything will have that 24fps movie look to it. As in any fast moving object not appearing to move completely smoothly but being able to discern the "frames". There is nothing bad in making your landing look like a film movie, but the low "framerate" could impact your ability to reliably track moving objects and increase your reaction time. When playing video games having the game run at lower than 30 fps has a very noticeable effect in that you don't see the result of your control input quite as quickly and leads to the game feeling less responsive and clumsier. While true that 24fps is the framerate where our eyes start seeing a sequence of images as continuous motion, but 24fps is not as fast as our eyes can see. We can typically see up to about 50Hz and this is why CRT monitors always scan at 50Hz or more. You can get around that by PWMing it at 100Hz, but you still wouldn't get much of a brightness difference, so the most noticeable effect would just be flickering trails behind very fast moving objects, or perhaps a bit of that "DLP projector" feeling if you move your head quickly. --- End quote --- You wouldn’t get the “24fps look”, you’d get annoying flicker instead. As someone who is sensitive to flicker, the 100Hz flicker of LED lighting dimmed from 50Hz mains is super annoying and distracting. For aviation this would be outright dangerous for me. As I’ve discussed in other threads on the forum, to fully eliminate ALL flicker artifacts in ALL conditions requires a PWM frequency of about 30KHz, at which point a non-PWM constant-current LED driver makes more sense, generally. (The “flicker fusion threshold” of 60Hz that’s usually accepted... well, it is true, but only for the comparatively slow, high-resolution center of the eye, and only when everything — head, eyes, and object being viewed — are perfectly still. Our low-resolution peripheral vision is much more sensitive to flicker, and as soon as anything is in motion, we need much higher PWM frequencies to prevent it breaking up into dots of light, known as the “phantom array” effect.) |
| jweir43:
--- Quote from: Nusa on June 10, 2019, 06:31:59 am ---If you are actually talking about LED landing lights (presumably aircraft certified), and they accept both AC and DC, that just means there is rectification going on inside the lighting unit to convert any AC sine wave to DC before it gets to the actual LED(s). I assure you that LED's are not AC devices. Light Emitting Diode. --- End quote --- You are kidding, right? Jim |
| Nusa:
--- Quote from: jweir43 on June 10, 2019, 03:15:06 pm --- --- Quote from: Nusa on June 10, 2019, 06:31:59 am ---If you are actually talking about LED landing lights (presumably aircraft certified), and they accept both AC and DC, that just means there is rectification going on inside the lighting unit to convert any AC sine wave to DC before it gets to the actual LED(s). I assure you that LED's are not AC devices. Light Emitting Diode. --- End quote --- You are kidding, right? Jim --- End quote --- Which part do you think I'm kidding about? Certification requirements for aircraft parts? http://www.faa-aircraft-certification.com/certification-of-aircraft-components.html (And virtually everything requires a logbook entry!) That LED's are diodes that emit light? I'll let you google that one. |
| Zero999:
--- Quote from: jweir43 on June 10, 2019, 01:47:26 am --- --- Quote from: Audioguru on June 10, 2019, 12:40:07 am ---I was taught that a fast pulse or pulses of light for durations less than 30ms appear to be dimmed. I am not talking about a slow incandescent light bulb. --- End quote --- You were taught wrong. Jim --- End quote --- No, he is right. The human eye acts like a low pass filter. Short pulses will appear dimmer, than long ones. Awhile ago, I did an experiment which involved putting short pulses, of hundreds of Amps through high powered LEDs. The flashes appeared to be dim, but would have been bright enough to cause eye damage, had they been continuous, assuming the LED would have survived, which of course it wouldn't.. |
| tooki:
Indeed, if our persistence of vision didn't perform a LPF effect, PWM dimming wouldn't work. |
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