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Human Eye -- Peak or Average Response

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edavid:
I don't know why people are messing with you.   The human eye has very close to average response, over a wide range of conditions.  So don't worry about DC vs. pulsed drive, it's not going to make a significant difference.

Someone:

--- Quote from: jweir43 on June 09, 2019, 09:14:36 pm ---I've got a white landing light of about twenty watts (DC power).  I shine the light at the ground when I'm about 350' AGL.  It lights a rough ellipse on the ground and lets me see whether or not there are animals on the runway before I collide with them.

I run the light on DC and get a particular illumination.  If I run the same exact device on AC of any frequency you want above the flicker level and I adjust the current so that the pulse width times the current gives me the same power into the light, will the light appear brighter to me as reflected from the SAME ground at the SAME altitude at the SAME attitude, at the SAME ....   In other words, the only differences is pulsed power versus DC.  Does the pulse width affect the result (right up to the maximum pulse current of the device)?  Is it any brighter at any combination of pulse width and current than at DC?

THat should take care of any test conditions, I hope.
--- End quote ---
It really doesn't provide enough information. The "enhancement" reported by various groups that you are chasing is highly dependent on the conditions under which the observer is viewing the test, and the absolute luminance observed and spectral characteristics etc.


--- Quote from: jweir43 on June 10, 2019, 01:42:12 am ---Oh, dear God.

I  can buy 50 watt LEDs if I can figure out how to heat sink them.

Your stuff about moving light sources and propeller sync have NOTHING to do with the question.  The LED is WELL outboard of the propeller.  PLEASE do NOT introduce extraneous problems as there are none.

You want a clean airframe?  Same problem; consider a glider.
--- End quote ---
You are missing the basic understanding of the problem to attempt chasing the last few percent. A pulsed source will cause artefacts to vision in that sort of application (looking through a propellor or not) unless you are pulsing way up into 10's of kHz or higher, I can not put a figure on the exact point because the information is missing. Trying to shoehorn LEDs into this application is almost certain to fail unless you have the background in optics which you haven't demonstrated.

Someone:

--- Quote from: edavid on June 10, 2019, 01:48:02 am ---I don't know why people are messing with you.   The human eye has very close to average response, over a wide range of conditions.  So don't worry about DC vs. pulsed drive, it's not going to make a significant difference.
--- End quote ---
It can make a big difference practically, or completely disorient the viewer if done poorly. But there are researchers who like to get publications by claiming significant improvements in apparent brightness (under very carefully controlled situations) and uneducated people try and extend that to making their lamps brighter (which will almost always never work and end up with a poorer result).

Berni:

--- Quote from: jweir43 on June 09, 2019, 09:14:36 pm ---Sorry, I though it obvious that I would have to get over the 24 Hz. flicker frequency to avoid the persistence of vision obstacle.  Let's say that you have your choice of any frequency from 25 Hz. to daylight.

Viewing angle is dead on boresight.

Empirical testing to follow.  It is a trivial experiment and one that I probably should have done instead of asking the question if anybody has done the experiment and how did it turn out?

Let me pose the question for what I **REALLY** want to know.

I've got a white landing light of about twenty watts (DC power).  I shine the light at the ground when I'm about 350' AGL.  It lights a rough ellipse on the ground and lets me see whether or not there are animals on the runway before I collide with them.

I run the light on DC and get a particular illumination.  If I run the same exact device on AC of any frequency you want above the flicker level and I adjust the current so that the pulse width times the current gives me the same power into the light, will the light appear brighter to me as reflected from the SAME ground at the SAME altitude at the SAME attitude, at the SAME ....   In other words, the only differences is pulsed power versus DC.  Does the pulse width affect the result (right up to the maximum pulse current of the device)?  Is it any brighter at any combination of pulse width and current than at DC?

THat should take care of any test conditions, I hope.

Jim

--- End quote ---

If your aim is to have a brighter landing light then the answer is no. Any potential difference is going to be tiny while causing more problems.

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.

Nusa:
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.

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