How is Light Produced - October 28, 2024

Luminous VS Non-Luminous

• Luminous

  • Luminous objects produce light on their own

    • E.g. light bulbs, a lit match and the Sun!

  • Light from Incandescence:

    • The production of light as a result of high temperatures

      • E.g. burner of a stove set to a high temperature; light from a burning candle, molten glass

    • Incandescent light bulb: tungsten filament glows as electricity going through the filament is converted to visible light, and the rest is converted into infrared light, which feels like heat radiating from the bulb → inefficient light source

• Non-Luminous

  • Non-luminous objects do not produce their own light → can only be seen by using reflected light

    • E.g. most objects around us: trees, books, etc.

Light From Electric Discharge

• The process of producing light by passing an electric current through a gas

  • E.g. lightning-lit “neon” signs (gases other than neon can be used)

• Various gases produce different colours:

  • Neon gas → red colour

  • Helium → gold colour

  • Argon → pale violet-blue colour

  • Krypton → greyish colour

Light From Phosphorescence

• The process of producing light by the absorption of ultraviolet light resulting in the emission of visible light over an extended period of time

  • E.g. glow in the dark objects are an example of phosphorescence

• The phosphor materials keep some of the UV energy and release the rest as visible light (lower energy)

Light From Fluorescence

• Fluorescence occurs when an object absorbs UV light and immediately releases the energy as visible light

  • E.g. highlighter pens, and laundry detergents: contain fluorescent dyes that cause clothes to appear brighter

• Fluorescent lights are the most common application of fluorescence

  • A fluorescent light tube is filled with very low-pressure mercury vapour → an electric current running through the tube causes the mercury atoms to emit UV light → UV light strikes the fluorescent coating of the tube to produce visible light

    

Light from Chemiluminescence

• Chemiluminescence is the production of light as a direct by-product of a chemical reaction

• Virtually no heat is produced - “cold light”

  • E.g. light sticks/glow sticks: two chemicals are originally separated in the stick → bending the stick causes the chemicals to mix, causing a chemical reaction that produces visible light

Light From Bioluminescence

• The production of light in living organisms as the result of a chemical reaction with little or no heat produced

  • E.g. certain bacteria, fungi, marine invertebrates, fish, glow-worms

  • E.g. firefly: a chemical reaction between oxygen and luciferin occurs inside the insect causing light to be produced!

Light From Triboluminescence

• The production of light from friction as a result of scratching, crushing or rubbing certain crystals (i.e. sugar)

  • No practical applications at this time!

Light From Light-Emitting Diode (LED)

• The production of light as a result of an electric current from a semiconductor, a material that allows an electric current to flow in only one direction (i.e. silicon)

• LEDs do not require a filament and do not produce much heat → more energy efficient than incandescent bulbs

  • E.g. indicator lights in electronic devices, Christmas lights, illuminated signs, traffic lights