While testing the ignition system on my car with a variable gap spark tester I noticed that the spark was orange. I suspect that there may be a problem with the ignition coil such that there is sufficient voltage to jump the air gap, but that not enough amperage to generate a nice blue spark.

While researching the color of air sparks, I came across this in a wiki on ionized air glow:

Rydberg atoms, generated by low-frequency lightnings, emit at red to orange color and can give the lightning a yellowish to greenish tint.

Might low amperage and Rydberg atoms be the reason for my sparks being orange?

I also ran across this Briggs and Stratton page which claims:

Orange and yellow come from particles of sodium in the air ionizing in the high energy of the spark gap

But the question would still remain why some air gap sparks are blue while others have this orange / yellow coloring.

If not, what might be another explanation for my orange sparks?


1 Answer 1


i have deleted my previous answer and agree with @RobertS.Barnes that the emission spectrum from nitrogen is a reason for the colouration although the spark is best when the colour of it is an intense white with colouration around the edges. This type of spark also appears to be the widest and indicates a large voltage across the gap producing a large current through the air.

  • $\begingroup$ But in the linked post on blue sparks they say the blue color is due to ionization of nitrogen atoms and subsequent deexitation, i.e. the blue light is generated with electrons fall back to a lower energy level. $\endgroup$ Commented Mar 21, 2016 at 9:54
  • $\begingroup$ I have changed my answer as a result of your comments. $\endgroup$
    – Farcher
    Commented Mar 21, 2016 at 10:15
  • $\begingroup$ But why am I observing orange sparks, not just blue ones? $\endgroup$ Commented Mar 21, 2016 at 10:42
  • $\begingroup$ How does this answer the question? Blue airglow is also due to nitrogen atoms/ions. $\endgroup$
    – ProfRob
    Commented Mar 22, 2016 at 14:10

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