Why do Christmas lights glow green near a Tesla coil?

[Willow Wanda]

Homework Statement

For a high school physics class, I chose to build a tesla coil for a real world application assignment. I was able to build it fairly easily and it turned out great. Before presenting to the class next week, I've been seeing its effect on different types of light bulbs and other household objects (some of them can look pretty cool). Most of the (non cfl) light bulbs ended up looking like plasma balls (caused by the ionized argon gas inside them i think?), however, when i hold christmas lights (and a few other small similar bulbs) nearby, they glow green instead of developing the purple streamers inside. What causes this bright green glow instead of the purple plasma streamers like the other bulbs? I've tried to research it but i haven't had much luck. Does anyone have any ideas?

Homework Equations

n/a

The Attempt at a Solution

Maybe caused by atomic emission spectrum of some gas inside?
I googled different spectrum and had some trouble though - I couldn't find information on what type of gas was inside the bulb, and I couldn't find any commonish gas that emits the bright neonish green light (maybe xenon? I can't really tell)

 

[berkeman]

Thread closed temporarily for Moderation...

 

[berkeman]

Thread re-opened. Thank you for your patience.

What kind of "Christmas lights" are these? Are they clear, or maybe they are green already? Are they incandescent? Did this happen when they are just loose bulbs, or only when they are connected to a wire string of bulbs?

 

[Willow Wanda]

any kind of christmas lights work (as well as a few older miscellaneous light bulbs that I've found in my basement - but they don't glow quite as bright). I've tried multiple brands and styles of white christmas lights (the small, clear, incandescent bulbs), and they all glow bright neon green in the presence of the high voltage. It works with both loose bulbs and strings of multiple bulbs

 

[gneill]

Incandescent lightbulbs are often charged with a low density inert gas (argon or nitrogen is typical) rather than trying to form and maintain a perfect vacuum.

 

[Tom.G]

and they all glow bright neon green in the presence of the high voltage.

That is a clue. The Northern Lights (aurora borealis) glow green and red/pink. https://www.google.com/search?&q=aurora+borealis

Although this site: http://www.aurora-service.eu/aurora-school/aurora-borealis/ says the Green is from Oxygen, not something you want in an incandescent lamp! So maybe this lead isn't so good after all.

Edit:
Or maybe it's an indication of leaky or cheaply made bulbs. Do larger new bulbs glow green or just old ones?

 

[Willow Wanda]

The smaller oval style light bulbs glow as well, but I can't find anything larger than that size that produces the same effect. The light bulbs I've been using aren't ancient; they're probably around 5 years old and have never been used. I haven't seen it work with any of the new light bulbs (even those of similar size and shape) that I've just purchased (other than the strands of christmas lights), however, this may just be a coincidence.

I've attached a pictures if that helps- Sorry for the poor photo quality, the spark gap produces rapid flashes of light that make it hard for the camera to focus

 

[Tom.G]

Yes, the picture helped. I sampled the Green in the image and got the following RGB values:
4C 5E 22
83 95 43
93 B3 52

Working with just the first and last sets, which were the dark and light areas, I normalized the numbers by:
subtracting the smallest (Blue) from the two other colors (to eliminate the Brightness variation),
convert to Decimal and normalize to 0-255 ( because a later step requires that; it also shows that the dark & light areas are close to the same color)
(4C 5E 22) - (0 0 22) = (2A 3C 0) to decimal-> (42 60 0) normalize-> RGB = (179 255 0)
(93 B3 52) - (0 0 52) = (41 61 0) to decimal -> (65 97 0) normalize-> RGB = (171 255 0)

From there, I used Spectra.exe (free download from http://www.efg2.com/Lab/ScienceAndEngineering/Spectra.htm) to match the RGB to Wavelength.
(179 255 0) = 555nm
(171 255 0) = 552nm
So look at the NIST (https://www.nist.gov/pml/atomic-spectra-database) site for spectral lines around those wavelengths.

 

[Willow Wanda]

Thank you so much for your help!

 

[Tom.G]

Oh, and remember that your camera color rendition may be a little off so those measurements can't be considered absolute, just ballpark within your camera capabilities.

It has sure gotten me curious, please keep us updated.

Cheers
Tom