Page 1 - Lesson note- Sources of light

SAI INTERNATIONAL SCHOOL
Class 6
Lesson Notes
Subject- Physics

Ch. – Light, Shadows and Reflection
Subtopic- Sources of Light

NOTES:
Sources of light: A source of light is an object from which light is coming out.
The kinds of sources of light that first become hot and then emit light are called hot
sources of light. E.g.-sun

The sources which emit light with their temperature not getting higher than the
environmental temperature are called cold sources of light. E.g. - LEDs, fluorescent
lights etc.

luminous objects: The objects that produce their own light are known as luminous
objects. E.g. - sun, blub, torch, candle, fireflies etc.

l The natural luminous objects are known as natural sources of light. E.g. - sun,
fireflies, etc.

l The man-made /artificial luminous objects are known as an artificial source of
light. E.g.- candle, bulb, torch, etc.

(Note: Non-luminous objects: The objects that do not produce their own light are
known as non-luminous objects. E.g.- tables, books, chair, moon, etc.)

(How do we see non-luminous objects?

Non-luminous objects reflect the light they receive from luminous objects. We see
a non-luminous object when light reflected by it reaches our eyes.
• When some non-luminous objects are heated to a high temperature, they may
start emitting light.
• E.g.- when metals are heated to a very high temperature, they become
luminous and emit red light.
• The planets in the solar system and their moons reflect the light of the sun
falling on them, and we can see them.)

A Brief History of Light and Light Sources:

• Ancient Times:
People used sunlight during the day and fire (like torches and oil
lamps) at night. The earliest light sources were natural, like the sun
and fire.

• Discovery of Fire (~1.5 million years ago):
A breakthrough that gave humans control over a light source at night.