Do LED lights flicker? (ac or dc current)

[sao123]

my new christmas tree lights are LEDs, and they do indeed flicker.
/thread.

 

[spidey07]

If you're talking about car brake lights, absolutely. It's highly annoying and distracting. Should be illegal IMHO. Causes tracers for me.

 

[Rubycon]

Originally posted by: Jeff7
Wow, I thought this was an old thread.



Flickering is subjective. Some people will complain about a 60Hz monitor flickering. Others have no idea that monitors even flicker.

You could probably solve the flickering with a few capacitors, or at least reduce it.

LEDs also can use pulse width modulation, which I think is for brightness control. I've seen quite a few LED brake lights on cars which flicker, and as far as I know, they have access to an easy source of DC.
I have no idea what a car's alternator puts out, but the battery (and its charger of course) are DC.

LED's have very fast attack (rise) and decay (fall) times so their outputs will closely track to input aberrations including the way they are driven if PWM frequencies are too low. Capacitance can act as a buffer to lengthen persistence for simple circuits. Decent lighting drivers will use PWM for dimming at frequencies sufficient that flicker is only noticed if the light is waved quickly from side to side, etc.

Most things in the home like LED displays and fluorescent digital displays used in microwave ovens and clock radios have their segments sequentially driven at high rates. A video camera with an adjustable electronic shutter reveals this nicely. If you have good teeth you can also crunch ice or hard foods like pretzels and see it too!

 

[DrPizza]

I demonstrate AC by using two LED's. At the end of a 5 foot cord, I soldered 2 different colored LEDs in parallel, but with a resistor in series to reduce the voltage to the LEDs. I plug the cord in & spin it around in a circle. Thanks to persistence of vision, you can see little arcs of red, then yellow, then red, then yellow, then red... Only one color is on at a time, and the light is brightest more toward the center of the arcs; it fades toward either edge. One of these days I'm going to use a digital camera during the demonstration, time the number of revolutions per second, # of colored arcs per revolution (camera helps here) and calculate the frequency of the supplied power.

 

[AlienCraft]

Originally posted by: ICRS
What is this lighting for if you don't mind me asking?

Also I wonder why MH (Metal Halide) lights aren't used to light homes and such, they have an efficiency rating that is higher or as high as any fluorescents. I think they give a nicer light too.

Simply put, heat. The "bulb" can shatter if damaged as well. They are used in outdoor / warehouse lighting where there is sufficient room for the heat effects to be mitigated.

 

[Rubycon]

Originally posted by: DrPizza
I demonstrate AC by using two LED's. At the end of a 5 foot cord, I soldered 2 different colored LEDs in parallel, but with a resistor in series to reduce the voltage to the LEDs. I plug the cord in & spin it around in a circle. Thanks to persistence of vision, you can see little arcs of red, then yellow, then red, then yellow, then red... Only one color is on at a time, and the light is brightest more toward the center of the arcs; it fades toward either edge. One of these days I'm going to use a digital camera during the demonstration, time the number of revolutions per second, # of colored arcs per revolution (camera helps here) and calculate the frequency of the supplied power.

That reminds me of this. :laugh:

And speaking of sausage-weiners - let's not forget the 230V hissing-farting weiner! 😀