Persistence Of Vision

So tonight I'm hanging out with my friend Nigel, and he's brought along one of his science toys—a little white plastic ball. Um, it's not actually a white plastic ball at all. You told me you were bringing the white plastic ball tonight. It's, uh, what color would you call that? I would call it, uh, purple.

"Purple? Really? You say purple?"

That I, you know, I don't—I'm not good with colors. I don't know if you want me to say fuchsia, but it's, you know, it's purple.

"Well, it's interesting you say that. Um, there is lighting there, but it is actually a red, blue, and green light, but it looks purple."

No, there's definitely a red, blue, and green light in there.

"All right, well, how are we going to settle this debate?"

I can show you that it is red, blue, and green.

"How are you going to do that?"

Um, by twirling it in a circle. Simple.

"You're going to twirl that in a circle, and all of a sudden I'm going to see that it's red, blue, and green? I promise you nothing less."

Okay, it's a pretty good promise. Let's uh, let's see it.

"All right, wow. Okay, so uh, I'm not too big of a person to admit when I'm wrong, and I see a red, green, and blue uh, balls around the outside of the circle, but when you slow it down, it goes back to being purple."

Yeah, it's um, actually everyone will see it being purple because the red, blue, and green lights are turning on and off so quickly after each other that your brain actually merges it into one color. When the ball is in one place, so the eye actually kind of holds the information there about what color it's seeing for an instant longer than it's there, and it merges together to produce that purple color.

"Yeah, that red, blue, and green kind of merge to this, Dusty violet color."

Dusty violet? Dusty violet, you know, your color should be a pain.

"Why can we see them separated when you swirl it in a circle?"

When I swirl it in a circle, I'm actually getting the ball to switch colors to red, to green, to blue at different points in space. So at different points in space, your eye is not actually holding that image as it switches to a different color.

"Right, so even if the eye remembers the color that it's seen, it's not going to merge with the next color because that occurs at a different point in space?"

Exactly. So it's much easier to see the red, blue, and green lights happening in the ball than it is when it's still.

"So can you think of uh, some practical applications for this?"

I cannot, but um, but it's a lot of fun for a Saturday night out, right?

"It is a lot of fun for a Saturday night out in a, um, in a dark alley."

Yeah, so try that at your next party.

"Next party trick? Yeah, it's a good party trick."

All right, well, let's go. A lot of parties, as you see.

"Let's go crash some parties. We are going to be a big hit with this thing."

High five!

"I'm not surprised that no one wanted to be interviewed by us."

"Oh, I am! This is awesome! This is awesome! This is awesome!"