The human body uses light-induced photochemical reactions on a daily basis. From the photosensitive cells in our eyes to the light-reliant vitamin D synthesis process in our skin, our bodies rely on and can use light in numerous ways. It stands to reason, then, that many cells in the human body may react to light. So how does light affect cells in the body, and how can it be used for the benefit of human health? That is the question behind the treatment method known as low-level laser therapy or photobiomodulation.