1. Light and its Properties

2. What is Light? Light is a form of energy that we can see.
Sources of Light:
Luminous Sources: Produce their own light.
Examples: Sun, stars
Non-Luminous Sources: Do NOT produce their own light but must have a luminous source shine on them to be seen.
Examples: Moon, earth, humans, cars
Note: Candles, lamps, etc are non-luminous sources until turned on (lit) – requires mechanical energy.
A luminous object is one that gives off light. In other words, it glows of its own accord.
To be able to glow, the object must have its own source of energy. A torch shines because of the energy stored in its batteries, whereas all stars shine using energy created by nuclear fusion. Both of these are considered to be luminous objects.
In order for us to see an object that is non-luminous, it must reflect some of the light it receives from a luminous source, such as the Sun. Most of the objects we see, such as cars, clouds or even the Moon, are not luminous; it is just that they reflect sunlight.

3. Properties of Light Light...
ALWAYS travels in a straight line (linear propagation).
Is invisible until reflected by translucent (partially transparent) or opaque objects.
Can be transmitted, reflected or absorbed by different kinds of matter (eg. Glass slide, mirror, book)