Strangely, not very dark at all.
The "year without summer" in 1816 was caused by the volcanic ejecta from Mount Tambora blocking a small fraction of the sunlight which strikes the Earth. Days and nights were marked by strange phenomena, such as spectacular sunsets caused by sunlight reflecting and scattering through the fine particles suspended in the atmosphere, but there are no remarks about not being able to see during the day, or nights being unusually dark.
Instead, there was a deep and lingering cold, which affected plant growth and caused widespread unrest throughout many nations as crops failed and hunger spread. Fortunately for us, this effect only lasted one year...
The Dinosaur Killer asteroid kicked so much particulate matter into the atmosphere that it was indeed dark for a short while (not just dust from the strike, but forest fires from the burning vegetation and water vapour blasted out of the ocean). The heavy particulate matter fell out rapidly, as you would expect, and even smoke from the fires dissipated quickly. After a period of days to perhaps months, the atmosphere would look clear to the unaided eye, but the ring particles are up there scattering the incoming sunlight and reducing the temperature.
Your biggest problem would not be light, but getting warm coat and finding a source of food.