How Does Light Affect the Body’s Internal Clock?

Have you ever wondered why you are active during the day and sleepy at night? Why are some animals like owls and mice the opposite? A big reason for this is called circadian photoreception, which is the way we synchronize the body’s internal, 24-h clock to the light cycle outside. This process starts in the eye. In this article, we discuss the characteristics of circadian photoreception and the scientists that helped us understand this process. We explore the key parts involved in circadian photoreception: photopigments, which are the pigments in the eye that change when they absorb light and are each found in their own cells. Last, we examine ganglion cells, which are special cells in the eye that send information to the brain.