A small primer on optical attributes of Light.
( — largely edited, 18-19 January 2014, originally from; Wednesday, March 27, 2013 at 3:58 pm UTC + 05:30 )
If you ever seem, to be caught up between: they say light always moves at the same speed-c, they keep on harping, why then, its energy so different; we have light of various energy and frequencies. One that are harmful, like x-ray or ultraviolet and one that are quite soft on us all. The answer is there are two kinds of speed, when it comes to vector emissions like light, one speed is on the plane of polarization, giving us the energy or frequency or intensity of light waves, and the other, the speed perpendicular to that plane, that is; the speed at which energy of light is transmitted across the galaxy, its this latter speed, which is slated to be known as speed-of-light (instead of, speed of light’s energy transmission vs speed that determines the energy value of light transmission) and always a constant known as c, whose value is unchanged, as long as a single quantum of light is considered and in vacuum.
Note that vector emission means there are 3 dimensions, in which this wave is created or propagated, light wave, its a plane + a perpendicular dimension to that plane. The plane is called plane of polarization which always contains two fields, Electric and Magnetic field, and the perpendicular dimension is the direction in which the energy of the light wave is propagated, therefore, gives the light-wave-speed; which are again of two definition, the physical or actual speed known as group velocity, and the virtual, conceptual speed of each wave train, known as phase velocity. This definition of phase and group velocity are always to occur; for any kind of waves and not just light wave. So, the light-wave-group-velocity (for a single quantum-of-light, called photon) is always c = 2.99 x 10 (8) meters/second, in vacuum.