The gravitational wave luminosity in the quadrupole approximation is obtained by integrating the energy flux from Equation (14) over a distant sphere. When one correctly takes into account the projection factors mentioned after Equation (2), one obtains 
Notice that the expression for is dimensionless when . It can be converted to normal luminosity units by multiplying by the scale factor× 1026 W, and that of a typical galaxy would be 1037 W. All the galaxies in the visible universe emit, in visible light, on the order of 1049 W. We will see that gravitational wave systems always emit at a fraction of , but that the gravitational wave luminosity can come close to and can greatly exceed typical electromagnetic luminosities. Close binary systems normally radiate much more energy in gravitational waves than in light. Black hole mergers can, during their peak few cycles, compete in luminosity with the steady luminosity of the entire universe!
Combining Equations (2) and (15) one can derive a simple expression for the apparent luminosity of radiation , at great distances from the source, in terms of the gravitational wave amplitude :matched filtering). This leads to an enhancement in the SNR, as compared to its narrow-band value, by roughly the square root of the number of cycles the signal spends in the detector band. It is useful, therefore, to define an effective amplitude of a signal, which is a better measure of its detectability than its raw amplitude: fluence, or time-integrated flux of the wave. As in many other branches of astronomy, the detectability of a source is ultimately a function of its apparent luminosity and the observing time. However, one should not ignore the dependence on frequency in this formula. Two sources with the same fluence are not equally easy to detect if they are at different frequencies: higher frequency signals have smaller amplitudes.
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