DC battery electric supply results in flickering L.E.D. ?

[sear]

Fluorescent lights may be more efficient (more lumens per Watt) than incandescent.
But at 60 Hz an incandescent filament may have enough thermal mass to not strobe. Fluorescent lights can strobe, and for that reason can be a poor choice for illuminating a machine shop. If the strobe frequency matches a machine's operating frequency, often a motor-driven machine, what may be rotating at 3,600 RPM might appear under fluorescent light to be motionless, appear to be turned off. It's not. And bad things have happened to good people as a result.
Some A/C L.E.D. lights are designed, engineered to not strobe. Good idea. It's easier on the eyes for extended reading and other tasks such as sewing.

But more inexpensively engineered alternating current light emitting diodes can flicker, even if too fast for the unaided human eye to detect.
The lights mentioned above can "strobe" flicker on, off, & back on again without a human observer noticing, due to human "persistence of vision". Persistence of vision is why a human can watch an old analog film movie at 24 frames per second, but instead of perceiving 24 consecutive progressive still images, perceives fluid motion.
The light flickers because the alternating current flickers.

Direct current or D/C electricity doesn't do that. A D/C powered L.E.D. shouldn't flicker because the D/C power that drives it doesn't flicker. Right?

I used to think so.

BUT !!

Check out the two following illustrations.

The first image is the display screen of a finger-tip "Pulse Oximeter". Your doctor might already have jammed one of these on your finger in the doctor's office. It displays %SpO2, an indication of how you're processing Oxygen.
The two or three digit number below displays heart beats per minute.
There's also a little bar graph that spikes for each heart beat, also graphically indicating the strength of that particular beat.



This first image shows what the human observer perceives, static display stability, varying only as the sampled parameters vary.

BUT !!
This second graphic shows what a UHD movie camera shows of the Pulse Oximeter in operation.
The Pulse Oximeter operates on internal battery power, D/C.



So if the Pulse Oximeter display operates on D/C power why would it flicker?

Or more to the point, how could it flicker?

Apparently the UHD camera plays a role in this. I've seen similar result on car lights in traffic. To my human eye I see no flicker. But review the sight from a UHD camera and some such lights clearly flicker substantially.
How can an electric light powered by D/C power source do this?

That it happens I have no doubt.
How it happens I have no clue.

You?

 

[Wolf]

Way, way over my head. I used to work in a Factory some many years ago before Fluorescent lighting was generally installed. At that time is was just a "blub" and to increase the ability to "see" clearly, you just upped the Wattage of the blub.
However the problem again IMHO is we speed ahead with new apparatus, before judging or checking what long term effects it has on us Humans.

 

[sear]

That is for SURE !
Behavioral psychologist BF Skinner prefaced his book Beyond Freedom and Dignity explaining:
we turn to technology to solve problems. BUT !! It seems so many of the problems we have today were considered solutions to previous problems.
Horses left too much poo poo on the road. No one ever died of that. BUT !! They just didn't care for it. So they invented the MG and the Rover. Problem solved? Sort of. Don't have to watch your step quite so carefully anymore. BUT !!
The atmospheric Carbon all those gosh darn automobiles belch into the planets atmosphere may raise mean sea level enough to put many millions under water. Plenty of people have died of that.

On our beloved incandescent days:
Pappy had a "man cave" apartment across the street from the U.N. in NYC. Hilarious. It was literally a one room apartment. It had a Murphy bed, which I though only existed in '50's vintage children's cartoons. It looked like a closet.
Anyway he noticed 40 Watt light-bulbs and 60 Watt light-bulbs cost the same to purchase (but not to operate. Not sure he considered that).
Today when I buy an LED * for my home, I have to use the incandescent Watt to lumens conversion chart on the box. Problem is, there's some information they don't include, like whether their A/C LED strobes or not.
My next door neighbor complained to me about eye fatigue while reading by compact fluorescent (CFL) lamp light. I tried to talk him into building his own uninterruptible power supply (UPS) and reading by 12 Volt DC light.
So he sold his house & moved away.

* I deliberately avoid fluorescent lights, because they have neurotoxic heavy metal in them.

 

[Wolf]

BUT !! It seems so many of the problems we have today were considered solutions to previous problems. Sear
I do so much agree, it's as though those "broadcasting" "we have solved the problem", are not thinking ahead as to the solution they have found, is only going to cause more problems. I am finding the same problems with so called "easy Mobile phones". The "young" have no problem is using and do so more or less "all their waking day", but I just wonder if, in some years time, those who use the Phones will be made aware of possible damage they are doing to their eye's and possibly radiation from the phone. Thank the powers I can still the old type of Handset and not have worries of walking into someone while "engrossed " on the hand held mobile phone.

 

[sear]

W #4

I've already read accounts of brain cancer in smart-phone users. The difference being, old fashioned Copper wire land-line telephones channeled the signal through primitive Copper wire, not at radio (cell-phone) frequency.

BUT !!

There are much deeper behavioral and sociological problems, including an unusual if not unprecedented social isolation, including:
Whereas decades before the smart-phone a person sending a message might telephone and exchange information including greetings in spoken speech, establishing and improving a rapport between them. Now it's abbreviated text.
A vivid visual example of this was a pic I saw of four humans seated at a small square table. Decades ago they might have talked, & perhaps drank & dined together there. BUT ! In the pic none of the four had direct eye contact with anyone else present.
Instead each of the four had full attention on their smart-phone.
In this way we members of today's Western society may not be developing their interpersonal skills to the same skill level as was the norm before the smart-phone.

That by itself might seem inconsequential.
Unfortunately there's a titanic difference between seeming inconsequential and being inconsequential. "Brave New World"? Braver than me it seems.