What Causes the Blue or Violet Color of St. Elmo's Fire?

💡 The Answer

• The color comes from excited nitrogen and oxygen molecules in the air, emitting visible light when they relax.
• Blue and violet wavelengths dominate because the discharge is low-energy, similar to a neon sign.
• Higher-energy discharges like lightning appear white or yellow due to heating of air to plasma temperatures.
• The exact hue depends on air composition, pressure, and humidity, but violet is common.