• Light travels at a speed of about 300,000 km/s

• It can travel around the earth 7.5 times in a mere one sec.

• This property of light is utilized in many technical applications such as optical communications which transfer huge data in a very short time.

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Speed of light

• Luminous objects- anything that gives off light of its own

• Non-luminous objects- visible because of light reflected from it.

• Natural sources of light: Sun, Stars, lightning

• Artificial light: is light made by humans: light bulbs, candlelight, fireworks

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Sources of light

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• Where there is no light there is darkness, we call this a shadow.

• The region of deep, total shadow is called the UMBRA and the region of partial shadow is called the PENUMBRA. The umbra is a region where no light can get to while the penumbra is a region where some light can reach. 

• Shadows explain lunar and solar eclipses.​

Shadow

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• Photometry is a branch of optics which deals with illumination and the amount of brightness that the light source possesses.

• Luminous intensity refers to the brightness of the light source, expressed in the unit candela (cd). The brighter the light source is, the greater its luminous intensity.

• The luminous energy emitted from the light source is called luminous flux and is expressed in lumens (lm).

Brightness of Light

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