How light travels

Light travels as waves. These are transverse waves, like the ripples in a tank of water. The direction of vibration in the waves is at 90° to the direction that the light travels.

Light travels in straight lines, so if you have to represent a ray of light in a drawing, always use a ruler.

Unlike sound waves, light waves can travel through a vacuum (empty space). They do not need a substance to travel through, but they can travel through transparent and translucent substances. The table summarises some similarities and differences between light waves and sound waves:

Light wavesSound waves
Type of waveTransverseLongitudinal
Can they travel through matter (solids, liquids and gases)?Yes (if transparent or translucent)Yes
Can they travel through a vacuum?YesNo
How are they detected?Eyes, camerasEars, microphones
Can they be reflected?YesYes
Can they be refracted?YesYes

The speed of light

Light travels extremely quickly. Its maximum speed is approximately 300,000,000 m/s, when it travels through a vacuum.

The very large difference between the speed of light in air (almost 300,000,000 m/s) and the speed of sound in air (343 m/s) explains why you:

  • see lightning before you hear it
  • see a firework explode before you hear it
  • see a distant door slam before you hear it