Derive Relativistic Beaming Equation: Learn Physics Easily

[Tahmeed]

While studying about some physics things, I came to know a term Relativistic beaming. I looked up in wiki and found a pretty decent article which gives you an equation where the real and apparent luminosity are related by a factor of (Doppler factor)^3-a where a is spectral index.
But where's the derivation of this formula? google didn't help me much, neither did some common textbooks of Undergrad levek.

 

[phyzguy]

Try Jackson, "Classical Electrodynamics", Chapter 14.