Sources of Light

Luminous: Objects that produce light; essential for vision in the dark.

Types of Luminous Objects

Incandescence:
- Light produced by heating metal.
- Example: Filament (wire) in a bulb glows when heated.
- Inefficient due to heat loss.
Electric Discharge:
- Light from electricity passing through gas.
- Seen in neon signs and lighting.
- Gas glows when energized by an electric current.
Fluorescence:
- Light emitted during exposure to UV light.
- Used in classrooms and office lights.
- Energy efficient and cool to the touch.
Phosphorescence:
- Light emitted slowly after UV exposure ends.
- Seen in glow-in-the-dark materials.
- Electrons store and release energy gradually.
Chemiluminescence:
- Light from a chemical reaction.
- No heat involved in producing light.
- Used in glow-in-the-dark sticks and forensic science.
Bioluminescence:
- Light produced by living organisms.
- Common in fireflies, jellyfish, and some fungi.
- Used for attraction, camouflage, or communication.
Triboluminescence:
- Light from friction or breaking crystals.
- Seen when rubbing or crushing quartz.
- Not understood well scientifically.
Light-Emitting Diode (LED):
- Light moving from a semiconductor.
- Very energy efficient and durable.
- Used in screens, signs, and bulbs.
Electroluminescence:
- Light from electrical current in material.
- No heat or filament required.
- Used in modern display technologies (OLEDs).
Organic Light-Emitting Diodes (OLEDs):
- Light from organic compounds under voltage.
- Thin, flexible, and bright displays.
- Used in smartphones, TVs, and wearables.
Plasma Displays:
- Light from ionized gas particles in a screen.
- Used in large flat-screen TVs.
- Replaced by LED OLED.
Laser:
- Light that's intense, focused, and single-wavelength.
- Used in surgery, cutting tools, and CDs.
- Highly directional and powerful beam.

Non-Luminous Objects

Objects that don't emit their own light.
Usable only when they reflect the source of light.