Brightness and darkness are a pair of antonyms, both of which describe the state of the objective world related to light. Brightness refers to the state in which the observer can observe the surrounding things well when the light is abundant, while darkness refers to the state in which the observer can not perceive the surrounding things when there is no light. Therefore, the so-called light should be some kind of carrier that can change the state of things around the observer, but it is not something that the observer can directly perceive. Therefore, on the one hand, what the human eye sees can not be the so-called light; on the other hand, the light should be some carrier that can make the objective things bright, so that the human eye can see these things in a bright state. The objective things that can be seen by human eyes and are in a bright state are objective entities composed of various atoms, and it should be a force that can change their state. It can be seen that the essence of light should be the carrier responsible for transmitting some kind of force, which is most likely to exist only between charged particles. Therefore, there is good reason to think that the essence of light is a collection of some carrier or carriers responsible for the transmission of Coulomb force. This conclusion can explain all the physical phenomena and experimental results related to light at the same time, which is the most realistic conclusion at present. Hope to get the attention and support of experts, scholars and friends at home and abroad.