How dark would the sun become if we traversed a Bok globule? Bart Bok gave his name to dust clouds of 2-50 solar masses, which by their darkness may be 100 times more frequent than telescopes can detect. 

If the solar system traversed a Bok Globule, how dark would the sun become towards the surface of the Earth, as visible by humans?
Not noticeably darker.

Assuming such a globule has a mass of 50 solar masses and a diameter of 1 light year, that would make it's average density about $2.2\times 10^{-16}\,kg\,m^{-3}$ which is fairly close to not being there at all in human terms.

An imaginary tube of this stuff 1 AU tall and of area 1 meter squared would contain about $3\times 10^{-5}\,kg$ of mass.  That is an imaginary tube from Earth to the Sun.

That much matter won't block much light.

For comparison the density of air at ground level is about $1.2\,kg\,m^{-3}$.  So less than a millimeter of air at ground level blocks more sunlight than the dust cloud would.

Also