Which prefix refers to "light" in a medical or scientific context?

The prefix "photo-" is derived from the Greek word "phos," meaning light. In medical and scientific contexts, this prefix is commonly used to describe processes or phenomena that involve light, such as photosynthesis in biology or phototherapy in medicine. When you see "photo-" in terms like "photophobia" (fear of light) or "photomicrograph" (a photograph taken through a microscope), it indicates a direct relation to light. This makes it the correct choice for indicating anything associated with light in these fields.

The other prefixes do not pertain to light. "Pneumo-" relates to air or lungs, "sarco-" refers to flesh, and "path-" signifies disease or suffering. Each of these pertains to entirely different aspects unrelated to light.