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
Constant voltage LEDs use something called Pulse Width Modulation, or PWM, to simulate dimmed lights. That’s basically what you’re describing.
I knew that dimmable LEDs exist now, but I didn’t know why they worked. Cool!
Like some motors they operate best at a certain duty cycle.
The issue with some really cheap ones is that it’s obvious.
It’s also why, if you’re so inclined at Christmas time, led string lights on trees are hard to photograph since you’ll catch some of them on while others are off at the time of the photo.
Duty cycle does not refer to the frequency of the flicker.
The frequency on a PWM light doesn’t change, it’s the same for the full range of control. What that frequency is, is determined by the controller generating the PWM signal, not the light.
PWM can be done at different frequencies. Cheap PWM controllers can only manage lower frequencies, those are the kind you notice and have trouble with in pictures. Good ones will run at frequencies so high, the fact they aren’t actually on continuously, will only matter in extremely high speed photography.
This is because a PWM controller can achieve the same reduction in brightness at any frequency. What matters is the fraction of time that the LED is lit each pulse. If you run the system at 1000Hz, half brightness means the flicker is 1000Hz, because you are sending 1000 pulses that are 0.5 milliseconds long. 75% brightness would mean the pulses are 0.75 milliseconds, but the number of pulses, and thus the frequency, is still 1000Hz. The flicker is the same.
Even at 99% brightness/duty cycle, a PWM light is still blinking at whatever frequency the controller is running at. Only at 100% does it not flicker, as 100% duty cycle means the controller simply keeps the light on continuously.
No matter what LED you use, they don’t usually care what the frequency is, nor what duty cycle you are at.
I’m not sure what you mean by motors running best at a given duty cycle, either. Sure, there is an efficiency peak, but the whole point of PWM is to be able to run something at any duty cycle you desire (resulting in the desired brightness for lights, RPMs for motors).
Modern night lights won’t have this happen, as they have a built-in “buffer” to prevent rapid on/off cycles like that.
But I do remember having an old night light when I was younger, probably from the late 80s, that you could make flicker by putting your hand in front of the bulb so that the light reflects back onto the sensor, effectively turning it into a very fast Useless Machine.
That’s how all ac powered lights work because the current is constantly alternating.
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
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.
