What is the speed of light?


Nothing can travel faster than the speed of light in a vacuum. Light always travels at the same speed in a vacuum in the form of a straight line and this constant speed is

c = 2.99792458 × 108 m s-1

Whenever light is in a vacuum, its speed, no matter who determines it, has the exact value. Even when the vacuum is inside a box in a rocket flying away from the planet, the speed of light passing through that box would be determined by both an astronaut in the rocket and a hypothetical observer on the planet to be exactly c.

In various materials

It scatters and is slowed down by the molecules in the substance as light passes through various materials. The amount by which light in a given material slows is defined by the refractive index, n.

Refractive index is defined as the ratio of the speed of light in a vacuum to its speed in a specific medium.

Refractive index (n) = c/v


  • n is the refractive index
  • c is the velocity of light in a vacuum ( 3 × 108 m/s)
  • v is the velocity of light in a substance

Law of reflection

When the light reflected from the medium or the surface, the angle of reflection depends only on the angle of incidence to the surface. According to the law of reflection, the angle of reflected wave reflected from the surface is always equal to the angle of incidence.


When light passes through a substance or medium, light gets a bend on the basis of the wavelength or frequency. This phenomenon is termed as the Refraction. It follows the Snells Law of Refraction.

Light Transmittance

When light falls on a substance, some light energy gets refracted and some gets absorbed by the substance. Light transmittance is defined as the fraction of incident light on the substance which passes through the substance at a particular frequency or wavelength.

Light transmittance is defined as the ratio of the intensity of the Incident light on the substance to the intensity of light which passes through the substance or comes out from the substance.

Wavelength of the light

Wavelength of Light is defined as the distance between the two consecutive crests or between two consecutive troughs. The Wavelength of the light ranges from 380 nm to 750 nm. In the electromagnetic spectrum, Infrared rays has higher wavelength than the visible rays and the ultraviolet rays has smaller wavelength as compared to the light.

Frequency of the light

The Frequency of light is defined as the number of crests which passes through a particular point in a second. It’s represented in hertz. The Frequency of waves is inversely proportional to their wavelength, which means that the higher the wavelength, the lower is the frequency and vice versa. The frequency range of the light is between 400 and 790 THz.

Colours in light

Light consist of different types of colours. These colours are differentiated on the basis of their wavelengths in the visible spectrum.  For example, when visible white light is made to pass through the prism, the different colours present in the visible white light bend at different angles depending on their wavelengths and as a result different colours of light are observed.

Light is radiant energy, an electromagnetic radiation that’s visible to the human eye, and is responsible for the sense of sight. It’s the most popular form of energy, the wavelengths visible to humans range between 380 nm  to 740 nm. It takes about seven minutes for light from the Sun to reach Earth. There are many sources of light a natural source of light is the sun as it plays an important role in our daily lives. Light behaves as a wave, it undergoes reflection, refraction, and diffraction just like any wave would.

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