Showerthoughts

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A "Showerthought" is a simple term used to describe the thoughts that pop into your head while you're doing everyday things like taking a shower, driving, or just daydreaming. The best ones are thoughts that many people can relate to and they find something funny or interesting in regular stuff.

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Night lights that detect light levels are probably flickering so fast that it just appears to be on (self.showerthoughts)

submitted 7 months ago by rockSlayer to c/showerthoughts

17 comments fedilink hide all child comments

Ok so I got this idea not while showering, but because I'm very high. The story does come from my bathroom though! I have a night light in my bathroom, and I was looking at the night light as I turned off the bathroom light. I'm a big nerd so I remembered that the things that detect light levels are actually diodes wired in reverse. I thought it would be funny to make it flicker by reflecting the light back on the diode, but it didn't work. That's when I had this realization

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[–] fidodo 13 points 7 months ago (2 children)

That's how all ac powered lights work because the current is constantly alternating.

[–] rockSlayer 4 points 7 months ago (1 children)

I was going to protest this, but then I started looking into how ac is converted to dc and realized that it would be cheaper to just let the diodes run on ac.

oh shit, my stoned ass wasn't prepared for this

[–] [email protected] 4 points 7 months ago* (last edited 7 months ago)

Indeed, older bulbs work in both directions and the voltage fluctuation isn't visible in the light emitted, because the thermal mass of the filament smooths out the alternating current into a continuous glow.

But LEDs will flicker unless the AC is rectified and smoothed out. Cheap lights will just not come with the circuitry to do this, as you can just hook up the diode directly, the only drawback being it will only emit light some of time. 60Hz is slow enough that you will notice it, however. Especially with movement, it makes reality look like it's running at 60fps.

Even when rectified, unless a capacitor is added to the circuit, LEDs will flicker. AC merely rectified will still have the voltage hitting zero 60 times a second, otherwise.

[+] [email protected] 2 points 7 months ago (1 children)

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[–] [email protected] 5 points 7 months ago* (last edited 7 months ago) (1 children)

While that's true, in between the voltage spike in either direction there is a moment of equilibrium that is equivalent to "off".

This moment lasts for too short a time to matter, as the voltage goes up and down smoothly in the pattern of a sine wave, meaning the time spent in the true "off" state is infinitesimally small, not 1/60 of a second as the frequency would suggest.

But even then the filaments temperature does fluctuate with the flips in voltage. It again just doesn't matter, as it becomes sufficiently energised again before it even cools enough to stop glowing.

Cheap LEDs stop glowing much quicker than a filament, which is why they can flicker even when the AC is rectified into DC, if done without a capacitor to smooth out the voltage.