a question about LED lights and power

[Backreefing]

Ok I’m laying around and thinking about LED lighting in perticular .
As many of us know these lights plug into our outlets which are AC @ 60 cycles per second. This power is converted into DC threw a bridge rectifier, but still has 60 peaks and dips per second . Thus shouldn’t the LEDs be flashing or pulsing @ 60 times per second ? This is faster than a human eye can see , we just see constant light .
This doesn’t apply to other forms of light because in floresant lights the gas in the tube gets exited by the current so probably no pulses. Metal halides use a headed element for light so also no pulses .
Which leads me to a question: has any of our members video recorded ( in high speed) a LED light ?
If the lights are pulseing I think it is easy to correct with the use of copasitors ?
Anyone have those cameras willing to try it and let us know ?
THX Backreefing

 

[MSB123]

I have. You can even do it with an iPhone. At 120 FPS.
I have not done it with aquarium LEDs. Only normal light style.

 

[Backreefing]

I have. You can even do it with an iPhone. At 120 FPS

What results? iPhone ( like in my hand I don’t know)

 

[jda]

I don't know the answer to your question about LEDs, but if I put my Canon 5d ay faster than 1/60th per second in a gymnasium with T5 lighting, then I can get dark shots.

 

[Backreefing]

I’ve been playing with my phone on slow motion setting and some sort of pulseing is happening. But a real camera will tell better.

 

[oreo54]

AFAICT all pulse.. Flourescents were horrible until they improved ballast circuitry to "up" the frequency..

Old fashioned (or very cheap) fluorescent bulbs flicker at twice the mains frequency if they use magnetic ballasts driven directly from the AC. Modern fluorescent bulbs use an electric ballast that runs at 5khz - 40khz (for CFLS), then the electrons stay excited for longer than the switching frequency and the light output is constant.

LED's will pulse esp w/ PWM dimming.. It dims with pulses..
Frequency is like 500 Cycles per second and on up..
When you dim this it will show up..

Switching power supplies "pulse" but at frequencies of

The rate at which the DC voltage is switched on and off during the pulse width modulation process in a switching power supply. The switching frequency in an inverter or converter is the rate at which the switching device is turned on and off. Typical frequencies range from a few KHz to a few megahertz (20Khz-2MHz).

Incandescent line voltage lights flicker..

Incandescent light bulbs flicker at twice the AC frequency, because the filament grows a bit hotter each time the current peaks. So: 50 Hz AC => 100 Hz flicker; 60 Hz AC => 120 Hz flicker.Jan 30, 2015

https://physics.stackexchange.com/q...licker-do-different-types-of-light-bulbs-have

Guess a simple answer is heated filament bulbs one can in effect smooth the flicker to the point of "almost" non-existant..
Others.. not so much.
It's complicated..
https://www.archlighting.com/technology/leds-fighting-flicker_o

Even the beloved incandescent lamp flickers. We don’t notice it, however, because thermal persistence, the same trait that makes incandescent lamps energy inefficient—about 90 percent of the electricity used is lost as heat—masks the effects of flicker. After the power is cut, the residual heat in the filament holds its glow until the next burst of power is delivered.

This isn’t the case for fluorescent lamps and LEDs, however. “These lighting sources react very quickly to power,” Benya says. “So when there’s no power, there’s no light.” In the 1990s, magnetically ballasted fluorescent lamps came under fire for their flicker. Manufacturers resolved the problem by moving to electronic ballasts, which operated the lamps above 20 kilohertz, well above the frequency at which people notice flicker.

https://www.archlighting.com/technology/leds-fighting-flicker_o

I think the large flicker in the MH and HPS assume magnetic ballasts..
LED's w/ constant current/constant voltage non-dimmed have minimal flicker..
Of course that also assumes clean power but as noted above DC power supplies have their own issues..
Though line driven w/ poor circuitry will prob. flicker.

 

[garbled]

I've heard the new AC (driverless) LED's flicker alot. Apparently there is some new tech out that smooths this out alot, but I haven't dug into those alot, as they don't come in colors that are useful to us yet. (that I know of)

 

[Backreefing]

This does in my opinion seams to be a aspect that needs improvement.
I don’t think it hurts corals but takes from the quality of the light . Example if the lights flickered at 60 hz then if this is eliminated then the LEDs could put significantly more light onto our coral . But the lights would have to be turned down?

 

[saltyfilmfolks]

Well, I’m not an electricial engineer. Honestly I don’t know how one would pull that off.


IMO , having seen some of the most glorious reefs under MH and knowing the arc is actually going on and off, I don’t belive it’s an issue.

 

[Backreefing]

In the case of LEDs a well sized and well placed capacitor would solve it. Buuuut that can change voltage to the LEDs and or affect the lights longevity. And probably affect PAR and lux as well.
I guess if one day I got an extra LED light and a local buddy to video it. Then it might be worth the experiment. Unless someone else is up to it then it’s tabled for now.
Thx for everyone’s input .

 

[arafas]

Hey I am an electrical engineer. I am pretty sure most LED light fixtures are PWM, therefore they do flicker correct. You have a good thinking not sure how corals would benefit from continues light source vs fast flicker. Your LED's wouldn't last that long if you didn't use PWM.

 

[oreo54]

Hey I am an electrical engineer. I am pretty sure most LED light fixtures are PWM, therefore they do flicker correct. You have a good thinking not sure how corals would benefit from continues light source vs fast flicker. Your LED's wouldn't last that long if you didn't use PWM.

Phillips Coralcare fixtures states they use current dimming..about the only one I know THOUGH it's not a commonly stated metric.

Others probably are PWM. Of course the frequency they use is unknown..
Aduino type (AtMega microprocessors ect) has limited adjustable frequencies and most seem to run at around 500Hz..
Limits of driver IC' s would also determine useable frequency.
Lots o little bits and pieces..

The frequency of the PWM signal on most pins is approximately 490 Hz. On the Uno and similar boards, pins 5 and 6 have a frequency of approximately 980 Hz. On most Arduino boards (those with the ATmega168 or ATmega328P), this function works on pins 3, 5, 6, 9, 10, and 11.

At 100% output is straight DC no pulses..
Frequency is adj. but limited in # and again gets into the driver IC thing...and some circuitry design things.
Like I said lots of little pieces..

There really isn't a "need" for PWM dimming over current control with proper thermal management.
Generally PWM is used to lessen color shifts caused by current changes..
Other reasons like current driver IC's use PWM more so than current regulation.

As a side note motor/fan control is usually in the 20KHz range for a number of reasons not really worth going into.
"I" believe the problem w/ using that for LED's is simply cost of circuit design..and prob more "little bits"..
I know some redundant text..oh well..
To lazy to clean it ATM......