Based on the fact that the frequency of light is reduced at the same rate (redshift) across a far distance, and the fact that the speed of light is constant, we can yield a mathematical law of light’s frequency loss. This law states for light traveling through vacuum space, its frequency must reduce an amount equal to Hu2092= H/MPC = 2.26*10^(-18) Hertz for every cycle (or every 1 wavelength of travel) of the light wave, where H is Hubble Constant and MPC = Megaparsecs = 30,856,775,814,913,673,000 km or Δf/f = -Hu2092t. This frequency is reducing exponentially against time (f(t) = fu2092e-Hu2092t). In Mathematics, some properties of Digamma function ψ(x) is used to deliver the law. By carefully comparing space’s expansion and this law of frequency loss, we conclude the expansion of space cannot be the reason of light’s frequency reduction, since they contradict one another. Instead, light traveling in space will lose a very small and constant amount of energy for every of its wavelengths that it travels. Finally an experiment is proposed to prove the theory and to find the Hubble Constant without needing to look at galaxies millions of light years away.