Sources of Light
Light from Incandescence
• light given off by an object because it is very hot -‐ Ex. A Conven@onal light bulb: an electrical current runs through
a @ny metal filament, making it hot -‐ Ex. The Sun
Over 90% of electrical energy from incandescent light bulbs is given off as heat!
Light from Luminescence
• Is the emission of light by a substance not resul@ng from heat
• It is a form of cold body radia@on. It can be caused by chemical or biochemical reac@ons, ac@vity of subatomic par@cles, radia@on or stress on a crystal.
Types of Luminescence
1. Electrical Discharge (Electroluminescence) 2. Fluorescence 3. Phosphorescence 4. Chemiluminescence 5. Bioluminescence
Light from Electric Discharge (Electroluminescence)
• Energy Sources: light given off by an electrical current passing through a material (typically gases)
• Ex. Lightening and • Neon Signs Note: Different gases emit different colours
L.E.D. (Light EmiXng Diode)
• Electric charge in one direc@on through a ‘semi-‐conductor’
• Recently -‐ different colours (including white)
• Far more efficient than Incandescent or Fluorescent
Fluorescence • A type of photoluminescence • Energy Source: objects absorb ultraviolet light energy (UV Rays that are invisible to the human eye) and rapidly releases them as visible light (known as photons) -‐ Ex. used on “black light” posters, t-‐shirts, body paint, etc. Blue Man Group -‐ Ex. Fluorescent coa@ng on the outside of fluorescent bulbs emit visible light
Phosphorescence • A type of photoluminescence related to fluorescence • Unlike fluorescence, a phosphorescent doesn’t immediately re-‐emit the radia@on it absorbs
• It is the delayed emission of photons that have been trapped in a ‘forbidden’ state
• Ex. Glow in the dark toys, paint, and clock dials that glow for some @me aeer being charged with a bright light (such as in a normal room light).
• Typically the glowing slowly fades out within minutes or up to a few hours in a dark room.
Chemiluminescence • Energy Source: results from chemical reac@ons
Bioluminescence
• Is a type of chemiluminescence • Involves biochemical reac@ons in living organisms
• Ex. Fireflies, angler fish, types of mushrooms, and more
Efficiency of light bulbs
L.E.D >> C.F.L. >> Incandescent
Light EmiXng Compact Fluorescent Diode Lightbulb