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11.2 The Production
and
Reflection of
Light
Light Emission
The sun is the earth’s primary source of light;
however many other things can also emit light
Luminous –ability to produce light
Non-luminous – does not produce light
Incandescence
The production of light as a result of high
temperature
(redOrangeYellowWhiteBluish white)
Example: Incandescent light bulbs , molten lava,
stove burner, candle
Electric Discharge
Producing light by passing electric current through a gas –
causes gas to glow
Examples: lightning, neon signs
Fluorescence
An object absorbs UV light, which it emits
IMMEDIATELY as visible light
Example: Black lights, fluorescent lights,
detergents, highlighters
Chemiluminescence
Emission of light through a chemical reaction
Little or no heat is produced; “cold light”
Example: Glow sticks
Bioluminescence
Emission of light by a living organism
through a chemical reaction with little
or no heat produced
Example: Fireflies, jelly fish, glow worms
Jelly Fish
Phosphorescence
Emission of light by a material after being
exposed to UV rays over an extended period of
time
Ex: Glow in the dark material
Triboluminescence
Emission of light by a material that undergoes
friction and/or the emission of light that results
from the breaking of certain crystals
Example: Eating lifesavers, tearing adhesive tape,
rubbing quartz crystals together
Light-emitting Diode
(LED)
Light produced as a result of electric current flowing through a
semiconductor
Semiconductor: a material that allows an electric current to
flow in one direction only. Example: Silicon
Doesn’t give off as much heat energy – no filament
More energy efficient
Examples: Christmas lights, indicator lights, traffic lights
11.2 Q’s #: 2-4, 5a, 7-11
11.2
2. Most of the electrical
energy it uses becomes
heat, not visible light.
3. Electric Discharge
4. Phosphorescent
materials turn absorbed UV
light into emitted visible light
over varying periods of
time, but fluorescent
materials do so
immediately.
5.a) No, they just make
clothes “glow” by
fluorescence in daylight.
7. Chemiluminescence is
called “cold light” because it
produces light, but virtually
no heat.
8. A light stick would be
relatively safe in an
explosive environment
because it produces
virtually no heat and cannot
cause sparks.
9. Organisms might protect
themselves from predators,
lure prey, and attract mates.
10. Compared to
incandescent bulbs, LEDs
produce little heat, do not
require a filament, and are
more energy efficient.
11. CFLs contain mercury, a health hazard
LEDs are more environmentally friendly,
however, are still more expensive than
CFLs
CFLs are considered a short term
replacement for incandescent bulbs until
LEDs become more economically
practical