Light Properties and Luminescence

• Light exhibits six main properties.
  • Travels in waves, as the electromagnetic spectrum shows.
  • Travels in straight lines, which shadows and sunbeams demonstrate.
  • Can be reflected, as seen in mirrors and water.
  • Can be refracted (bent), which happens via lenses and liquids.
  • Is a form of energy, carried in packets called photons.
  • White light comprises all rainbow colors which prisms demonstrate.

Sources of Light

• Light comes from different types of sources.
  • Bioluminescence: Light produced by living organisms, without heat.
  • Incandescence: Light emitted due to heat.

Types of Luminescence (Light without Heat)

• Include Fluorescence, Phosphorescence, Chemiluminescence, and Bioluminescence.
  • Fluorescence: Light emitted from exposure to electromagnetic radiation.
  • Phosphorescence: Light emission continues even after removing the radiation source.
  • Chemiluminescence: Light caused by a chemical reaction.
  • Bioluminescence: Light naturally produced by organisms.
• Glow sticks and fireflies produce light via chemiluminescence and bioluminescence.
• Shadows and their formation illustrate light's behavior and travel.

How Light Interacts with Materials

• Light interacts with materials mainly through absorption, transmission, and reflection.

Transparent Materials

• Allow all light to pass through.
  • Examples include clear plastic and windows.

Translucent Materials

• Allow some light to pass, often scattering it.
  • Examples include frosted glass and wax paper.

Opaque Materials

• No light passes through; light is either absorbed or reflected.
  • Examples include wood, metal, and concrete.

Reflection of Light

• Law of Reflection: Discovered by Euclid (c. 300 BC), the angle of incidence = angle of reflection.

Mirror Types

• Plane mirrors produce upright, same-size images.
• Concave mirrors (curved inward).
  • Inverted image if object is far.
  • Upright and magnified if object is close.
    • Example: makeup mirrors.
• Convex mirrors (curved outward).
  • Image appears smaller, upright, and farther away.
    • Used in car side mirrors and security mirrors.

Refraction of Light

• Refraction involves bending light as it moves from one material to another with different density.
  • Light slows down in denser materials (e.g., glass, water), bending towards the normal.
  • Light speeds up in less dense materials (e.g., air), bending away from the normal.

Lenses

• Unlike mirrors, which reflect.
  • Double Convex (Converging): Rays come together, and image can be inverted and magnified.
    • Used in eyes, magnifying glasses, and microscopes.
  • Double Concave (Diverging): Rays spread out, creating a smaller and upright image.
    • Used in flashlights and headlights.

Telescopes

• Refracting: Convex objective lens collects light; convex eyepiece magnifies.
• Reflecting: Objective mirror collects light; eyepiece magnifies it, with best magnification achieved with a longer image-lens distance.
• Binoculars: Use two reflecting telescopes; prisms shorten the path by reflecting light.

Microscopes

• Objective lens forms an image, and the eyepiece magnifies it further.

Eye Anatomy & Function

• Cornea: Outer layer that refracts light.
• Aqueous humor: Fluid between the cornea and iris.
• Pupil: Light entry hole, size controlled by the iris (adjusts to light).
• Lens: Focuses light; shape controlled by the ciliary muscle (thicker for close, thinner for far).
• Sclera: White outer layer.
• Vitreous humor: Jelly inside the eye, maintains shape.
• Retina: Light-sensitive layer where the image forms.
• Optic nerve: Sends signals to the brain.
• Blind spot: No light sensors where the optic nerve connects.
• Tapetum lucidum: Reflective layer in some animals for night vision.
• Eyelid = shutter, Retina = film, Cornea = glass, Iris = diaphragm, Ciliary muscle = focus ring, Pupil = aperture.

Vision Problems

• Myopia: Can’t see far; corrected with a concave lens.
• Hyperopia: Can’t see close; corrected with a convex lens.
• Astigmatism: Blurry vision from irregular cornea/lens; fixed with asymmetric lens.