Most of us have seen those mysterious, silent flashes of light from an almost indeterminate direction, seen only at night. Most people call it heat lightning.
But there really is no such thing as heat lightning. That is to say, what we call heat lightning is not actually a different sort of lightning. Rather, it is the flashes of regular lightning being reflected off clouds at night that gives us those eerie flashes. It is silent because it comes from so far away that sound waves are dampened before reaching our ears. But the light from lightning, being more efficient than sound, sometimes bounces off clouds and travels great distances, sometimes well over 50 miles, before reaching our eyes.
This so-called heat lightning is never seen in daylight because sunlight outshines it. But when the clouds are lined up just right, we see the flash of lightning many miles away.