What Is Heat Lightning?
Heat lightning is simply the usual kind of lighting which is discharging beyond the horizon. The light from the distant flash reaches our eyes, but the thundering sound is too far away for us to hear. Heat lightning is often seen on hot summer evenings.
A flash of lightning is actually a big electric spark. Lightning occurs when a huge amount of electrical energy builds up in a thundercloud. Then it discharges all at once. The hot spark splits the air with a thunderous crack. The flash we see in the sky is caused by hot, glowing air in the lightning channel.
The term “heat” in heat lighting has little to do with temperature. Since heat lightning is most likely to be seen in association with air mass thunderstorms in the warm season, the term “heat” may have been used because these flashes are often seen when surface temperatures are warm.