Vision – Basics

Basics

Definition of Light

Light is visible electromagnetic radiation that can be perceived by human eyes (also known as visible spectrum).

Light is made up of photons which is compliant with both corpuscular theory and wave theory. In other word, light has wave-particle duality. Light can travel through vacuum, air, water and transparent materials.

As for the range of wavelength of visible light, there is no clear boundaries. Normally human eyes can perceive light wavelength between 380 to 740 nm

Spectrum

Light ColorWavelength(nm)Typical Wavelength(nm)
Red625–740 nm700
Orange590–625 nm620
Yellow565–590 nm580
Green500–565 nm550
Cyan485–500 nm500
Blue450–485 nm470
Violet380–450 nm420

Reflection of light

Reflection of light is the change in direction of light at an interface between two media and return back to where it is originated.

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1. Specular Reflection

Specular reflection is the process when a collimated beam is emitted to a surface, the reflected rays are still paralleled. The reflective surface is smooth, for example, like mirror and calm water surface.

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2. Diffuse Reflection

Diffuse reflection is the process when a collimated beam is emitted to a surface, the reflected rays are at many angles rather than being paralleled. The reason is at reflective spot of each ray, the normal line is in different direction. The reflective surface is coarse, for example, like wood and concrete.

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Refraction of Light

Refraction of light is the change in direction of light when passing from one transparent medium to another. Similarly with reflection, refraction occurs at the interface between two media. The only different thing is refraction rays go into another medium while reflection rays return back to where they are originated. Because the speeds of light in two media are different so the direction of rays changes at the interface.

At the interface between two media, refraction and reflection occurs at the same time. The speed of reflection light is the same as that of incident light but that of refraction light is different.

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Diffraction of Light

Diffraction of light is the process that light bends and continues propagating when encounters an obstacle or an aperture. The longer the wavelength is, the easier diffraction occurs.

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