Light is important for vision, plant photosynthesis, and vitamin D production in animals. It travels in straight lines and can be refracted, dispersed into a rainbow spectrum, or focused by lenses. The document discusses the properties, roles, and forms of light including sunlight, artificial light, refraction, dispersion, rainbows, the Newton disc experiment, lenses, and early theories about light and prisms.

1. Light : What is Light ?

2. Importance of Light
• Sunlight powers all light on earth,
either directly or indirectly. Plants
obviously must have sunlight or full-
spectrum artificial light to manufacture
their food by photosynthesis.
• For diurnal species (species that are
active during the day), light is
important for many reasons.
Obviously, it is required for vision, and
most birds have highly developed
sight. For many species of animals,
full-spectrum light is required for the
conversion of cholesterol to vitamin D.
• People living in northern cities that
are overcast for long periods of time
and receive little sunshine typically
report depression.

3. Properties of Light
• The Reticulate Property of light: Light travels in a straight line.
• The speed of light is 300 million meters per second in a vacuum.
• Refraction means that light bends when it passes from one medium
to another.
• When light enters a denser medium from one that is less dense, it
bends toward a line normal to the boundary between the two media.
• Dispersion is another property of light. This refers to the ability to
break white light into its constituent colors.

4. Role in our daily lives
• Study the picture given
alongside. This is Danish
Architecture.
• Danish Architecture depends
wholly on the direction of light
Look at the pic. Given
alongside. His life is
lightless.
Imagine living in a dark
tunnel forever…..

5. Rainbow : Another form of light
• Although light looks
colorless, it’s made up of
many colors-red, orange,
yellow, green, blue, indigo
and violet. (VIBGYOR)
• These colors are known as
the spectrum.
• When light shines into
water, the rays of light
refract, or bend, at different
angles.
• Different colors bend at
different angles--red bends
the least and violet the
most.
• When light passes through
a raindrop at a certain
angle, the rays separate
into the colors of the
spectrum-and you see a
beautiful rainbow.

6. Newton Disc
• Newton disc is a disc
with segments in rainbow
colours.
• When the disc is rotated,
the colors fade to white.
• In this way Isaac Newton
demonstrated that white
light is a combination of
the seven different
colours found in a
rainbow.

7. Time for a whole new concept.
The Prism.
In optics, a prism is a
transparent optical element
with flat, polished surfaces
that refract light.

8. The different theories of the prism’s
action on light.
Before Isaac Newton, it was believed
that white light was colorless, and
that the prism itself produced the
color.

9. Thomas Young
Augustin - Jean Fresnel

10. Lens – Convex
• Lens such that a
beam of light passing
through it is brought
to a point or focus.
• A lens which has at
least one surface
which curves
outwards.
• These lens are
thinner at the edges
and are thicker at the
center.

11. Lens - Concave
• A concave lens is thinner at
the center and thicker at the
edges
• Also called diverging lens.
• These lens are such that a
parallel beam of light
passing through it is caused
to diverge or spread out.

12. Credits