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Visual Systems I

Properties of Light

Light and Vision

  • The visual system uses light to form images.

  • Light = type of electromagnetic radiation visible to the human eye.

  • Electromagnetic radiation comes from many sources (radio, phones, X-rays, sun).

Properties of Electromagnetic Radiation

  • Electromagnetic radiation = wave of energy.

  • Main properties:

    • Wavelength = distance between peaks/troughs.

    • Frequency = waves per second.

    • Amplitude = height difference between peak & trough.

  • Energy ∝ frequency: higher frequency = more energy.

Frequency and Energy Examples

  • High frequency (short wavelength, high energy):

    • Gamma rays, X-rays (<1 nm).

  • Low frequency (long wavelength, low energy):

    • Radar, radio waves (>1 mm).

  • Visible spectrum = 400–700 nm.

Color

  • White light = mix of visible wavelengths (Newton, 18th century).

  • Single wavelength = appears as one rainbow color.

  • Red/orange (“hot”) = longer wavelength, less energy.

  • Blue/violet (“cool”) = shorter wavelength, more energy.

  • Color is a brain perception, not a property of light itself.

Optics and Light Interactions

  • In a vacuum, light travels in straight lines (rays).

  • In the environment, light rays interact via:

    • Reflection (bounce)

    • Absorption (energy transfer)

    • Refraction (bending between media)

  • Optics = study of these interactions.

Reflection

  • Light bounces off surfaces depending on strike angle:

    • Straight on → reflects straight back.

    • 45° → reflects at 90°.

  • Most objects we see = reflected light.

Absorption

  • Light energy absorbed into particles/surfaces.

  • Example: skin warms on sunny day.

  • Black surfaces: absorb all visible wavelengths.

  • Pigments: absorb certain wavelengths, reflect others.

    • Blue pigment absorbs long, reflects short (~430 nm) → perceived as blue.

  • In retina: photoreceptor pigments absorb light → trigger membrane potential changes.

Refraction

  • Bending of light when passing between transparent media.

  • Example: leg in pool looks bent.

  • If ray enters straight → no bend.

  • If angled → bends toward perpendicular line.

  • Caused by different light speeds in media (faster in air than water).

  • Greater speed difference → greater refraction.

  • In the eye, cornea and lens refract light → focus images on retina.