Have you ever jumped into a swimming pool thinking it was shallow only to realise it’s actually a lot deeper than you thought? Or have you gazed down into the ocean from a boat above thinking the fish are a lot closer than they actually are? An object seen in the water will usually appear to be at a different depth than it really is, but why is this? It’s all due to amazing process called refraction. Abernethy Owens is the Optometrist families trust for the best eye care solutions. If you are intrigued by refraction, read on to discover more about what it is and how it can change the way we see things.
What is Refraction of Light?
Refraction is the bending of light as it passes from one substance into another. The human eyes depend upon this bending of light, without it, we wouldn’t be able to focus light onto our retina. Refraction also makes it possible for us to have glasses, lenses, cameras, binoculars and is responsible for some natural phenomena including rainbows.
The amount of light bending depends on two things:
- Change in speed – different substance densities cause light to speed up or slow down more, this will make it bend/refract more.
- Angle of the incident ray – if light is entering the substance at a greater angle, the amount of refraction will also be greater. On the contrary, if the light is entering a substance head-on, the light will still slow down, but it won’t change direction.
Refraction of Light in Water
When light travels from air into water, it will change its speed and its direction. As light travels into a denser medium (water), the light ray will 'bend' toward the normal. When it goes back into the less dense medium (air), it will bend back through the same angle as when it came in.
Place a straw in a cup of water – when you look at the straw from a certain angle, it appears to bend at the water's surface. This is due to the change in density of the medium and therefore, bending of light rays as they move from the air to water.
Why Objects in Water Appear Closer than They Actually Are
When we observe objects in the water, they appear to be much closer to the surface than they really are. This is because refraction causes an illusion of the actual depth of an object in shallow water when observed from the bank or from a boat above. Light rays reflected from the object are refracted at the surface of the water, however our eyes and brain trace the light rays back into the water as though travelled away in a straight line, and not refracted at all. This results in an image of the object that appears at a shallower depth to where it really is.
Refraction in the Eye
Vision relies heavily on the ability of the eye to refract light. This takes place at both the cornea and the lens of the eye. People with vision problems often have a refractive error, which means that light rays are not bending as they should when they pass through the lens. This causes distortions with how objects are perceived.
If you are having trouble seeing clearly, make an appointment for a thorough eye examination with Abernethy Owens today. Proudly WA owned and operated for over 90 years, our experienced team can help with all aspects of Optometry. Make an appointment with us today.