Light and Optics Light and Optics Light is the passage of energy through space in the form of electro-magnetic radiation. It is in the form of particles which are called photons.
Photons travel at a constant speed, which is entirely unchanged by the motion of any observer.
The speed of light is almost exactly 300 megameters per second. Photons have no rest mass, and probably don't even exist at rest, and they have no electrical charge. Every single photon has a characteristic color which can vary if the observer is moving toward or away from the light source. Moving toward a source makes the light more bluish, and moving away makes it appear more red. Different colors happen because atoms have different sizes, different nuclear charges, and influences on each other when they are close together.