Light travels in straight lines outwards from its source

Light is produced by a source and travels outwards from the source in straight lines and all directions at 300,000 km/s.

Because we can’t actually see light travelling, we depict this property in diagrams that show light travelling in straight lines called rays. These rays travel out from the source until they hit something. Depending on the properties of whatever they hit, all or some of the rays will pass through it, bounce off it or be absorbed by it.

Only a vacuum allows the completely free passage of light. Some light energy is always absorbed by any material through which light passes. Thicker samples of the same materials absorb more energy, for example, objects are seen more clearly through a thin layer of glass than through a solid glass block.