Dear Tom,
On a road trip through Ohio we witnessed a cloud-to-ground lightning strike on the highway. The resulting flash of light was a spectacular shade of red. What caused the bright red color?
— Holly Robertson, Grayslake
Dear Holly,
Valparaiso University’s Bart Wolf offers three explanations for the colors in lightning. First, the temperature in a lightning bolt can vary, affecting its color — blue when hot, red when cooler. Second, certain colors may be blocked by dust, rain, hail, etc. as light travels from the lightning to our eyes. This may lead to varied hues. Third, and most plausible, is “ionization” (the breakdown of air’s gases into ions) resulting from lightning’s heat (50 thousand degrees). Ionized oxygen and nitrogen emit blue light. Ionized water vapor appears red due to hydrogen.
