Light as Rays - Optics Step by Step

A ray is a simple model of light's direction. In this model light travels in straight lines until it meets a surface.

optics Rays are not tiny sticks of light. They are a geometry model for direction, useful when wavelength effects are too small to matter.

Example

A ray is a simple model of light's direction. In this model light travels in straight lines until it meets a surface. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

A ray is a direction model

A ray is not a tiny object flying through space. It is a line we draw to track the direction light travels. When the setup is much larger than the wavelength, this straight-line model is useful.

\text{ray} \Rightarrow \text{direction of light}

In one medium the ray stays straight

In a uniform medium, the ray keeps going in the same direction until it meets a surface. That is why the ray model uses straight lines to track where light goes.

\text{same medium} \Rightarrow \text{straight ray}

Several rays can model one beam

A ray diagram can use more than one line for the same light beam. Those lines are bookkeeping directions; they are not separate little particles of light.

\text{ray bundle} \Rightarrow \text{several tracked directions}