Optics and Light Sources: Comprehensive Notes

Introduction to Optics

What is Optics?

• Origin: The term "optics" originates from a Greek word signifying "appearance" or "look."
• Definition: Optics is a branch of physics dedicated to studying the properties and behavior of light.
• Opening Activity: Brainstorming session to identify optical devices and applications of light in medicine, scientific investigation, environmental applications, and everyday items.

What is Light?

• Light as Energy: Light is a visible form of energy.
• Wave Properties: It exhibits properties and behaviors characteristic of a wave.
• Electromagnetic Radiation: Light is a form of electromagnetic radiation, involving vibrations of electrical and magnetic fields through space.
• Production of Light: Light is produced when excited electrons transition from a higher energy orbital to their stable ground state (lower energy level).
• Emission of Energy: The energy difference is emitted as a visible wave. Different energies correspond to different colors.

Sources of Light

Incandescence

• Definition: Light emitted from a hot body due to its temperature.
• Example: Incandescent light bulb (inefficient, with ~95% of energy used as heat).

Bioluminescence

• Definition: Light produced and emitted by a living organism as a result of a chemical reaction, converting chemical energy to light energy.
• Examples: Fireflies, glow worms, angler fish.

Chemiluminescence

• Definition: Light produced from a chemical reaction without a rise in temperature.
• Examples: Glowsticks, "Glo" necklace.

Fluorescence

• Definition: Light produced by the absorption of radiation at one wavelength followed by immediate re-radiation, usually at a different wavelength.
• Examples: Fluorescent lights, CFLs (more efficient than incandescent, with 80% of energy used as heat).

Phosphorescence

• Definition: Light energy is stored and then re-emitted slowly over a long time.
• Examples: Glow in the dark toys.

Triboluminescence

• Definition: Light produced by friction or crushing.
• Examples: Wintogreen Lifesavers, duct tape.

Light-Emitting Diode [LED]

• Definition: Transforming electrical energy directly into light energy; a small electric current can cause semiconductor materials to emit light.
• Examples: Electronics devices, new Christmas lights.

Electric Discharge

• Definition: Electric current is passed through air or another gas.
• Examples: Lightning, neon signs, plasma ball.

Natural vs. Artificial Light Sources

Natural Sources

• Examples: Electric discharge (lightning), bioluminescence (fireflies), incandescence (sun).

Artificial Sources

• Examples: LEDs, chemiluminescence, electric discharge (neon signs), incandescence (Edison bulbs), fluorescence (light bulbs).

Fluorescence vs. Phosphorescence

Similarities

• Both involve absorbing energy and then re-emitting the energy as light.

Differences

• Fluorescence emits light immediately, while phosphorescence emits light over a long period.
• Fluorescence emits light only as long as energy is provided (e.g., electricity).

Incandescent, Fluorescent, and LED Lighting

Incandescent

• Advantages: Cheapest bulb cost.
• Disadvantages: Most energy is wasted as heat, highest energy cost.

Fluorescent (CFL)

• Advantages: Not as expensive as LED, more energy efficient than incandescent.
• Disadvantages: Contains mercury vapor, requires special disposal.

LED

• Advantages: Most energy efficient, longest life, and lowest cost (including energy) over the life of the bulb.
• Disadvantages: Higher initial cost of replacing bulb.

Choice of Lighting at Home

• LED bulbs are recommended if higher initial costs can be accommodated, as they last the longest, cost the least in energy, and waste the least electrical energy.

Light Bulb Comparison

Energy Use

• Incandescent: 60W
• CFL: 13W
• LED: 6W

Energy Distribution

• Incandescent: 90% of energy released is heat.
• CFL: 80% of energy released is heat.
• LED: 75% of energy released is heat, channeled into a heat sink.

Estimated Lifetime

• Incandescent: 750-2,000 hours
• Halogen incandescent: 3,000-4,000 hours
• Compact fluorescent (CFL): 7,500-20,000 hours
• High power white LED: 35,000-50,000 hours

Cost Analysis (over 50,000 hours)