* Matter: Light can be bent when it passes from one medium to another, such as from air to glass or from water to air. This is called refraction. The amount of bending depends on the difference in the refractive indices of the two media.

* Gravity: Light can also be bent by gravity. This is called gravitational lensing. The more massive an object, the more it will bend light. This effect is only noticeable for very massive objects, such as black holes.

* Magnetic fields: Light can also be bent by magnetic fields. This is called the Faraday effect. The strength of the bending depends on the strength of the magnetic field.