Can't we just give these guys a light meter ? £15 at Amazon, problem solved, no faith needed.
How can a light meter or any other instrument prove to a born blind person that light exists?! He has no idea why the meter is beeping or moving or whatever. Why should he believe that it is because of some mysterious and strange thingy called light that exist everywhere?! He can do that only on blind faith.
Suppose there is a village full of blind people who have never seen anything for generations. They will live normally as though light does not exist. Their lives will be tailored around their capabilities. If one of them happens to visit another village with normal people he will relate tales of people who have supernatural abilities and strange visions of the world. The other blind people could be in awe of such new people or they could treat them as charlatans and liars.
If suddenly one of the blind people himself sees some flashes of light that the others don't see, they will treat him either as a delusional believer or as a superior prophet.
Even today we take many things on blind faith.... in scientists.....(both because of their authority and because lots of scientists together agree). Most astronomical details are taken on faith. Most people have no background in science and maths and no access to telescopes. We rely only on scientists. Dark energy, Dark Matter, the big bang, Singularity....are all taken on faith. We have no idea if these things actually exist or maybe even prove to be wrong in course of time.
Therefore faith is either blind based on what others say.....or faith can be based on ones own intermittent experiences of subtle phenomena.