Photons are the carriers of optical information. They propagate through media taking on properties associated with waves. At surface boundaries they interact with matter, behaving more as particles. They can also be absorbed by the retina, where the information they carry is transcoded into electrical signals that are subsequently processed by the brain. It is only there that a sensation of color is generated. In computer graphics, traditionally take a simplified view of how light propagates through space. Photons travel along straight paths until they hit a surface boundary and are then reflected according to a reflection function of some sort. A single photon carries a certain amount of energy, which is represented by its wavelength. Simulating light by tracing rays takes care of the physics of light, although it should be noted that several properties of light, including, for instance, polarization, diffraction, and interference, are not modeled in this manner.