Post by Mark Lloyd Post by trader_4 Post by Mark Lloyd
Post by gregz
Holiday lights flash 60 times a second, 120 if off a bridge rectifier.
The flashes are the same length. Without the bridge rectifier, every
other flash is dark (LEDs don't emit light when reverse biased).
60 or 120 times a second seems like a very high rate. It's the refresh
rate of displays. I'm surprised you'd even see it or that it would
be the desirable kind of flashing for holiday lights.
I didn't SEE it. That doesn't mean I don't know it's happening.
BTW, I have heard it. Once I replaced the microphone of an audio
recorder with a solar cell, and got to listen to the frequency of light.
It sounded about right for 120Hz.
There are a bunch of issues here.
A regular led that emits light at the color you see, when operated
off rectified AC, will have an intensity waveform that looks similar to
a 120 Hz. sinewave. The string of xmas tree lights may do that.
The white lights you buy for home use have a phosphor.
Some have a short-persistence phosphor and you can see the effects of
the flicker. Look at an AC powered fan and you may be able to see
the beat frequency in the pattern.
Some have a long-persistence phosphor that tends to smooth out the flicker.
Turn on your LED and let it warm up.
Turn it off.
If the light goes off instantly, you'll probably experience
If the light fades over a few seconds, you probably have a
long-persistence phosphor and will not see as many flicker artifacts.
You could do the same thing with a capacitor, but one big enough to
do much good wouldn't fit inside the bulb and would raise cost