Here's why:

* It's not actually lightning: Heat lightning is a misnomer. It's not a separate type of lightning. It's actually regular lightning happening far away.

* The distance is key: The sound of thunder travels slower than light. When lightning strikes very far away, the light reaches you quickly, but the sound of thunder may be too faint or travel too far to be heard.

* It's often associated with warm weather: Heat lightning is commonly seen on warm evenings, but this is just a coincidence. It's not caused by heat.

So, while it might look like lightning, it's just the light from a storm that's too far away for you to hear the thunder.