Light Sources and Receptors

• Light source: Any body that emits light towards the eye of an observer

Types of Light Sources

• Primary sources: Bodies that produce light themselves
• Natural sources exist in nature, such as the sun, stars, fireflies, and lava
• Artificial sources: Sources created by humans
• Examples include lamps, screens, and car headlights
• Secondary sources do not produce light but reflect and diffuse part of the light they receive
• Examples include the Moon and mirrors

Light Receptors

• A light receptor is any body that is sensitive to light or undergoes transformations
• Biological receptor is an organ that captures light in a living being
• For example, the human eye, photoreceptor cells of the retina (cones and rods), and plant leaves (chlorophyll)
• Electroluminescent receptor captures light and transforms it into electricity
• Examples include solar panels, photovoltaic cells, and camera light sensors
• Chemical receptor is a substance that changes under the effect of light
  • For example, photographic plates (silver film), pigments used in photography, and chlorophyll in photosynthesis

Dispersion of Light

• Dispersion of white light occurs when white light decomposes into several colours when passing through a prism
• Continuous spectrum of light: All the colours visible after the dispersion of white light
• White light is a mix of several colours: red, orange, yellow, green, blue, indigo, and violet
• Monochromatic light: Light that does not disperse through a prism

Propagation of Light

• The principle of rectilinear propagation of light: Light propagates in a straight line in a transparent and homogeneous medium

Mediums of Light Propagation

• Transparent medium: A medium that allows all light to pass through and allows clear viewing
• For example, clean glass and clear water
• Translucent medium: A medium that allows some light to pass through, but vision is not clear
• For example, frosted glass and tracing paper
• Opaque medium: A medium that completely blocks light
• For example, a wall or a piece of wood

Luminous Ray

• Any straight path followed by light, represented by a straight line with an arrow indicating the direction of propagation

Luminous Beam

• A luminous beam is a collection of light rays
• Convergent beam: Rays approach each other at a point
• Divergent beam: Rays move away from each other
• Parallel beam: Rays remain parallel to each other
• Speed of light propagation is very rapid
• In a vacuum, it travels at 300,000 km/s