Heat lightning represents a lightning that is seen near the horizon without the sound of thunder, because the thunder associated with the lightning is too far to be heard. In simple language, heat lightning is a lightning without thunder. It is important to note that lightning and thunder are not the same, nor can they be used interchangeably. They stand alone in meaning but are associated with one another: lightning is a flash of light; thunder is a loud noise that is facilitated by lighting and comes after lightning.
Nonetheless, this weather event got its name because it usually occurs when the climate is hot and humid, especially in the summer. Even though heat lightning occurs mostly in the summer, it is not unusual for this event to take place at anytime of the year. It occurs during thunderstorms, rainstorms, snowstorms, thundersnows, sandstorms, or any other storms that produce lightning. Moreover, heat lighting can occur before, during, and after a storm. In fact, it is a good predicator of upcoming storms.
Despite its given name, heat lightning is not a unique form of lightning but rather a normal lightning that fails to produce thunder. Thus, it is soundless - only producing a flash (or flashes) of light. The flash that one sees is from a far-away lightning reflected off of the clouds and dust in the atmosphere. A couple of reasons for the lack of thunder are as follows: (1) the thunderstorm occurs too far away to be heard and (2) the wind in the atmosphere distorts and refracts the sound of the thunder.
The first reason is obvious, simply because it deals with the proximity and distance of the person to hear the thunder. This occurs with all sounds, whether it be from a human, animal, or a natural occurrence, because the closer the sound is to one's vicinity, the reception will be audible (unlike one who is afar). Likewise, it only makes sense that a person closer to a storm would hear its thunder than a person who is situated miles away. According to scientists, thunder rarely travels more than ten miles, so one who is located outside of that area will most likely not hear the thunderous sound.
The second reason, concerning wind influence, is evident because it has the power to change the atmosphere, including how thunder is heard. Because molecules in the air help reduce sound, the higher pitched airwaves are diminished. When one hears thunder at distance, he/she hears the low pitched of the thunder because the predominant sound is reduced by the wind. When one is farther away, the thunder becomes inaudible. Temperature and sound wave can also influence the sound of thunder.
Heat lightning, which usually occurs when the climate is hot and humid, is not a special type of lightning. Rather it is a normal lightning that fails to produce thunder; as a result, it is a silent lightning that is only seen and not heard. It is visible in thunderstorms, snowstorms, thundersnows, and other storms. Heat lightning is not secluded to a specific area, it can happen everywhere and at any time of the year.