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The Myth
Heat lightning isn̵7;t actually a distinct type of lightning. It̵7;s just regular lightning produced by a distant thunderstorm. The storm is so far away that you can̵7;t hear the thunder that the lightning produces, only see its flicker.
Origins of the Term
The term heat lightning probably originated during the era before air conditioning, when people would sit on their porches on hot summer evenings, because the air outdoors was cooler than the air indoors. Weather radar reports weren't yet accessible to most people, so they had no way of knowing there were far-off thunderstorms responsible for the lightning. People likely coined the term heat lightning because it was usually warm outside on the evenings that they noticed this phenomena.
The Facts
Think of seeing heat lightning as akin to seeing a tall mountain in the distance -- thunderstorm cloud tops reach 30,000 to 60,000 feet into the atmosphere. At night, lightning produced by these clouds is visible up to 100 miles away. Like stars, heat lightning can̵7;t be seen during the day because the light from the sun obscures it. The effect of heat lightning can be amplified when there is a layer of haze, as the haze reflects the light. Sometimes, you may begin to hear thunder from the storm producing heat lightning -- this means the storm is moving in your direction.
The Science Behind the Phenomenon
On average, thunder is only heard within about 10 miles of the source of lightning. Considering that the emanated light is visible from much further away, this is the most ordinary explanation for the phenomenon of heat lightning. However, the extent of sound waves in the atmosphere may vary depending on conditions such as air density and temperature, which change with altitude. This can cause sound waves to refract, or bend, in unusual ways, producing areas devoid of sound and making the lightning strike seem strangely silent.
Chance of Ground Strikes
Because heat lightning is essentially just ordinary lightning, it can strike the ground. Most lightning, however, tends to stay within a cloud or a group of clouds rather than hitting the ground. Meteorologists estimate that only about 20 to 25 percent of all lightning bolts take aim at the earth. But if heat lightning does strike the ground, in most cases, it will strike so far away from you that you won̵7;t even know it.