10.1 Sources and Nature of Light Image from: http://www.lazerkraze.com/masonoh/lk1images/lasertagss4.jpg
Light Emissions For all light sources, atoms absorb some form of energy. Excited atoms release energy, often in the form of light. Image from: http://s.hswstatic.com/gif/laser3.gif
Light from the Sun H atoms fuse together to form He (fusion reactions). Energy released from fusion excites gas atoms on outer layers. Excited atoms emit light. Image from: http://www.iceagetheatre.ca/research/nuclearfusion/nuclear_fusion_sun.jpg
Light from Incandescence Incandescence = light emitted from material because of high temperature Incandescent light bulbs have tungsten (W) wires. 95% of electrical energy released as heat. Image from: http://news.heartland.org/sites/default/files/imagecache/heartlander-thumb-promo-large/light_bulb_0.jpg
Light from Electric Discharge Sodium vapour bulbs (some streetlights) have Na + a small amount of Hg vapour inside. Electric current moves between electrodes at each end, exciting gas atoms. Image from: http://www.pgecurrents.com/wp-content/uploads/2011/06/LED-Street-Lights-Before-Watsonville-300x199.jpg
Fluorescence Fluorescent bulbs are coated with phosphor & have Hg vapour inside. Electric current excites Hg atoms, which emit UV light (not visible). Phosphor absorbs UV & emits visible light (phosphorescence). Image from: http://www.periodictable.com/Samples/080.20/s13.JPG
Efficiency of Fluorescent Lights Image from: https://ecoterramedia-ecoterramedia.netdna-ssl.com/wp-content/uploads/GE-100W-lumen-comparison-chart.png 20% vs. 5%
Uses of Fluorescence Image on left from: http://www.reptilescanada.com/gallery/data/500/medium/IMG_1029.JPG Image on right from: http://www.specialdays.com.au/img/att/11/img-11139-1394674660-a.jpg
Luminescence Luminescence is light generated without heating an object, e.g., fluorescence. Phosphorescence is light emitted due to exposure to UV light, that continues to be emitted. Image from: http://images.wisegeek.com/glowing-jellyfish.jpg
Chemiluminescence Light generated by energy released in a chemical reaction. Image from: http://g03.a.alicdn.com/kf/HTB124JlIXXXXXXsXpXXq6xXFXXX0/glow-stick-flashing-bracelet-lighting-flash-sticks-festival-products-10pcs-lot-colors-mixed-Outdoor-adventure-Life.jpg
Bioluminescence Light produced by living organisms due to chemical reactions in the living cells. Image from: http://www.robotspacebrain.com/wp-content/uploads/2014/01/bioluminescent-beaches-1.jpg
The Nature of Light Light energy travels in electromagnetic waves (involve electric & magnetic fields). Wavelength = distance from one crest of a wave to the next Image from: http://www.srh.noaa.gov/jetstream/remote/images/emwave.gif
Electromagnetic Spectrum Image from: https://multiphaseism.files.wordpress.com/2013/05/electromagnetic_spectrum.jpg