What are these interesting lights?

November 13, 2024 11:47 AM

Some friends and I saw what looked like mini Halloween or Christmas lights, strung over some bushes as decoration. The light was solid orange, but when we walked by, or even just moved our heads, a green glow appeared behind or alongside each one. It wasn't an afterimage - it was clearly something that was coming from the bulbs. They didn't change color on their own, or twinkle or fade or have any other effects.

I'd really like to find some of these, not necessarily orange and green, but small lights where a different colored glow appears with movement. Is this something anyone is familiar with, or can suggest a search that would find them?

posted by still_wears_a_hat to Home & Garden (10 answers total)

I don't quite understand your description, but something that might match this can happen when RGB LEDs are showing mixed colors (i.e., not pure red, green, or blue) and they're not doing their PWM fast enough. But it would be a little weird for orange to show up this way as green, since generally it would have the red elements on for more of the time than the green ones.
posted by aubilenon at 12:05 PM on November 13 [5 favorites]

Reflection from the green shrubbery?
posted by SPrintF at 12:12 PM on November 13

When I move my head, I see the color separation in these cheap LEDs; they're not actually a solid color, they're flickering a mix of colors like the RGB elements on a TV screen. The flicker on cheap ones is slow enough that your eye is catching only the green LED on at that point in your head movement.

The RGB color for orange is 255 red, 165 green, 0 blue -- so your eye is seeing just the red flash at one point in your head movement and the green at another point, so they're not overlapping and mixing.
posted by AzraelBrown at 12:29 PM on November 13 [7 favorites]

I came here to say what AzraelBrown suggested - they are LED lights that use color addition to create orange light. If you move your head you can see the colors separately instead of on top of each other. Try this interactive website:

Physics Classroom RGB Color Addition Interactive

If you mix 100% red with 60% green you get a nice orange color. I'm guessing that you notice the green light more than the red one because the colors look more different.
posted by amf at 12:34 PM on November 13

Yup, LED lights. There's a large color-changing set that's up year-round in my neighborhood. They're currently on static orangey-yellow and there's a very noticeable color separation into red and green in each bulb that moves down the line of lights as I walk past. The green is much more obvious to me, the red doesn't stand out as strongly.
posted by EvaDestruction at 1:19 PM on November 13

Response by poster: Thanks. I understand about color separation, and maybe that's it, but I'm not convinced. It was very distinct and a specific green. LED lights are all over, and I've never seen anything at all like that. I'm kicking myself that I didn't try to take a photo.
posted by still_wears_a_hat at 1:25 PM on November 13 [1 favorite]

There are often three tiiiiny single-color LEDs in a cluster in each unit -- red, green, and blue -- and when you move, you can actually juuuuast make out the gap between the emitters. The units themselves can be just a centimeter across, though, so the gaps are subtle.

An example: https://www.adafruit.com/product/2686
posted by wenestvedt at 1:37 PM on November 13 [1 favorite]

I had a set of cheap LEDs where you can adjust the color via an app on your phone-- I set them to an in-between shade of greenish and they glint reddish when you move your head. Drove me crazy, had to throw them out.
posted by The otter lady at 2:58 PM on November 13 [1 favorite]

Do either of you wear glasses? Sometimes mine do an annoyingly good job of color separation all on their own.
posted by Citizen Cane Juice at 3:31 PM on November 13 [3 favorites]

Yeah, anybody nearsighted enough can use the edges of their glasses for spectrum analysis. Purple LEDs are the most obvious, since they're always a red and blue one together - purple viewed straight through, but moving away from the center, each diverges into a red-and-blue pair.
posted by Rash at 8:50 PM on November 13 [3 favorites]