Optics

• Optics is the branch of physics that studies light, its behaviour, its interaction with matter and optical instruments.
• Light is electromagnetic radiation and does not require a material medium for propagation.
• Visible light is the part of the electromagnetic spectrum normally detected by the human eye, approximately 380-700 nm.
• The exact visible limits vary with the observer and viewing conditions; some references extend the red limit towards 760-780 nm.
• Visible light lies between ultraviolet radiation at shorter wavelengths and infrared radiation at longer wavelengths.

Luminous and Non-Luminous Objects

• A luminous object produces its own light, such as the Sun, a candle flame or an electric lamp.
• A non-luminous object is seen because it reflects or scatters light from another source.
• The Moon is non-luminous; it shines by reflecting sunlight.
• An object becomes visible only when light emitted, reflected or scattered by it enters the eye.

Wave-Particle Duality