When light moves from one medium to another, it can be transmitted through, absorbed by, or reflected from the new medium. Transmitted light may be refracted as it passes through the medium. These phenomena explain how we perceive objects and determine their colors, and whether they are opaque, transparent, or translucent.

1. When light proceeds from one medium into
another, (e.g. from air into a solid substance), several
things happen.
Some of the light radiation may be transmitted
through the medium. Transmitted light may
undergo refraction.
Some will be absorbed.
Some will be reflected at the interface between the
two media.
These phenomena explain the how we perceive
objects and determine their colors or if they are
opaque, transparent or translucent.
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2. Refraction: light is bent
Light
Transmitted
Medium
Index of refraction
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3. Index of refraction:
,
Medium
The index of refraction determines the degree
of bending of light as it passes through the
medium. The higher the n, the higher the
degree of bending. Read more
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4. Refraction
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5. permittivity of a substance
permeability of a substance
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6. Refraction
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7. dielectric constant
is the ratio of the permittivity of a substance
to the permittivity of a vacuum
relative magnetic permeability
is the ratio of a substance to the permeability of
a vacuum
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8. Reflection: light bounces back
Light
Refleceted
Medium
Reflectivity
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9. Reflectivity: R
I0
IR
Medium
The reflectivity determines the amount of light
reflected. The higher the reflectivity, the greater
the amount of light reflected.
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10. Reflection losses for lenses – remedy:
coating surface with very thin layers
of dielectric materials
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11. Absorption: light is absorbed
Light
Absorbed
Medium
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When is light absorbed?
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12. Conduction band
When
electrons
absorb light, Band gap
they jump to
a higher
energy level. Electron Valence Band
Light
Electrons can only jump if energy
absorbed (from the beam of light) is high
enough to cross the band gap.
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13. Transmission: light is transmitted
Light Transmitted
Medium
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14. Color
An object is perceived as light
from it reaches our eyes. The color
discerned is a result of specific
wavelengths that are reflected by
or transmitted through it.
Why is ruby brilliant red?
Why is gold gold? Why is silver
silver?
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15. from sapphire to ruby
addition of impurities makes the material absorb
wavelengths different from the original material
Silver and Gold
Silver is silver because when it is exposed to white light, it
reflects almost all of the light.
Gold is gold because some of the energy associated with light
photons having short wavelengths is not reemitted as visible
light.
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16. Opaque, Transparent and Translucent
Materials that are capable of transmitting
with relatively little absorption and reflection are
transparent – one can see through them.
Translucent materials are those through
which light is transmitted diffusely; that is, light is
scattered within the interior, to the degree that
objects are not clearly distinguishable when
viewed through a specimen of the material.
Those materials that are impervious to
the transmission of visible light are opaque.
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17. Metals are opaque and
highly reflective.
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