I'm NOT crazy! (At least not about this.)

WARNING: NERD POST AHEAD. POSSIBLE PHYSICS AND/OR BASIC ELECTRICAL THEORY.

Those of you who know me fairly well have heard of my twitchy eyes. If you haven’t, blah blah blah meningitis blah blah smacked my head on the floor blah blah my eyes have a really low frame rate when I move around blah blah torsional nystagmus.

Anyway, one interesting side effect is that I seem to be much more sensitive to lights blinking or changing very quickly. For example, I can almost always pick up the rainbow effect from DLP TVs, even relatively new ones. I’m a lot better at picking up on scan lines on CRTs, and so on. So when I first saw LED Christmas lights on a house in the dark, I could swear they had a 60 Hz flicker to them.

(If you’re still reading this and that doesn’t mean anything to you, here’s a quick explanation: the power in your house is Alternating Current, meaning the current switches directions—and in America, it does that 60 times a second, or 60 Hertz.)

The first time I saw it, I said to myself, “self, there’s no way those are flickering like that... they HAD to have put some sort of rectifier circuit or AC-DC converter on the line. No way they were that cheap or lazy.” (Non-nerds: see bottom.)

We were in Highland Park looking at Christmas lights last night, and I took a few long exposures. Imagine my surprise when I get back to my computer and start looking at the pictures. Here’s a long exposure of some standard incandescent Christmas lights:

Note the smooth, continuous lines, since the lights stay lit. Even though they technically turn on and off 60 times a second, the response of the filament inside the light is slow enough that it continues to light. Now compare that with a similar picture of some LEDs:

Notice anything? I left those incandescent lights in there for comparison. The LEDs actually show up as a series of dots because—you guessed it—they’re turning on and off. And how fast, you ask? It just so happens the above exposure is 0.4s, and each light shows up 24-25 times, which means they’re flashing at a frequency of 60 Hz. Math—it’s not just a good idea, it’s the law.

(For the non-nerds: There are two basic types of power delivery: AC, or Alternating Current as we discussed above, and DC, or Direct Current. DC just provides a voltage and does not alternate it with respect to time like AC.

Normal light bulbs are basically resistors that dissipate energy by turning it into heat and light. Like other resistors, incandescent bulbs don’t care which way the current flows through them—they take the energy and turn it into light either way. So even though the current comes and goes 60 times a second, the filament stays hot enough in between that it still emits plenty of light.

The D in LEDs, on the other hand, stands for Diode, which is an electrical component that only allows current to flow through in one direction; it’s perfect for DC power, but not ideal for AC, since when the current goes the wrong way, the diode won’t let it through. DC power is also common in electronics, which is where we get those lovely “wall wart” power supplies—those are taking AC power and converting it to DC power to be used by the electronics.

That circuitry to convert AC power to DC isn’t super expensive, but it’s not free. It you’re trying to make LED lights and you want to stay as profitable as possible, you can get away with just using AC and knowing that your lights light up only half the time. Unfortunately, that’s what this particular manufacturer did, to the detriment of people with googly eyes like me.)