Light is an electromagnetic radiation which belongs to visible range in electromagnetic spectrum. Visible range is the range of wavelengths of the radiation visible to human eye.
The speed of the light in vacuum is approximately . This value is universal constant and the motion of source, nature of source and anything else do not affect it.
Einstein’s special theory of relativity is based on the fact that speed of light in vacuum is independent of any factor.
Dependency of the speed of light in a medium:
(i) The nature of source does not affect the speed of light. Speed of the wave depends on the properties of the medium, not on the source.
(ii) For all the isotropic mediums, the speed of light is independent in the direction of propagation.
(iii) The speed of light is independent of the motion of the source relative to the medium, but the relative motion of the observer and the medium affect the speed of light.
(iv) Light is an electromagnetic radiation which propagates in the medium as a wave, and speed of a wave depends on the wavelength, thus, speed of light depends on wavelength.
(v) The intensity of light has no effect on its speed.