How we see

This lesson covers: 

  1. How light allows sight
  2. How a pinhole camera forms images
  3. The role of lenses in focusing light
  4. How light transfers energy to absorbers

We see things because light reflects into our eyes

Illustration showing light rays emitted by a luminous object reflecting off a non-luminous object and entering the eye.
  1. Luminous objects emit light rays.
  2. These light rays reflect off non-luminous objects around us (e.g. a book)
  3. Some of the reflected light enters our eyes, allowing us to see.

The pinhole camera demonstrates how images are formed

A pinhole camera is a simple device used to form images using light.

Diagram showing how a pinhole camera forms an upside-down image with light rays passing through a pinhole.
  1. Light travels from an object in straight lines through a small pinhole into the camera.
  2. As light crosses over inside the camera, the image seen is upside down.

Lenses refract and focus light

Diagram showing how a convex lens refracts and focuses light rays to a point.
  • Lenses refract light rays that pass through them.
  • Convex lenses bulge outwards and converge (focus) light.

How the eye sees light

Diagram showing how the eye sees light, including the cornea, lens, iris, retina, light rays, and image formation.
  1. The transparent cornea provides main focusing in the eye.
  2. The adjustable lens fine-tunes the focus for objects at different distances.
  3. The iris controls how much light enters the eye.
  4. Images are formed inverted on the light-sensitive retina.

Light transfers energy to absorbers

Image showing a camera and an eye as examples of light energy absorbers.

Light waves carry energy which is absorbed by detectors.

Absorbers convert this light energy into chemical and electrical signals.

  1. In the eye, these signals are detected by the retina and sent to the brain allowing sight.
  2. Digital cameras generate electrical charges representing the image.