Light does not travel on dark matter. Dark matter is a type of matter that does not interact with light or other forms of electromagnetic radiation, which is why it is called “dark” matter. It does not emit, absorb, or reflect light, so light cannot travel on or through it.
However, the presence of dark matter can affect the way that light behaves as it travels through the universe. Dark matter exerts a gravitational force on surrounding matter, including light, which can cause light to bend or be distorted as it passes through regions of high dark matter density. This effect is known as gravitational lensing and is one of the ways that astronomers can indirectly detect the presence of dark matter.