The phrase "faint light" refers to a very weak or almost invisible source of light. It means that the light is very dim or not very bright. Full definition
We train our telescopes on small patches of sky for long spells, trying to drink in as much faint light from distant objects as possible. (newscientist.com)
There was a little faint light at the end of the tunnel. (cindyandjana.com)
The unveiling of the human genome almost 7 years ago cast the first faint light on our complete genetic makeup. (science.sciencemag.org)