# Strength of gravitational waves vs. electromagnetic waves

If the recent gravitational wave's energy had reached us as visible light, how bright would it have been? Stackexchange complains about the form and brevity of the question so i add something... if it is strong enough to move a heavy mirror albeit by a 10000 th of a proton it should be quite strong and intuitively the light of even a bright star shouldn't have that strength.

In that vein, then, a good representative is the first observation, GW150914, which emitted an energy of about $E=3.0\:M_\odot c^2$ in about $\Delta t=0.1\mathrm{\:s}$ at a distance of some $L=440\:\mathrm{Mpc}$, which comes down to an energy flux of $$I=\frac{E}{4\pi L^2 \Delta t}\approx 0.23 \:\mathrm{\mu W/cm^2}.$$ This is equivalent to a weak light source, but it's probably visible by naked eye under suitably dark conditions.