Ah. OK. But why not just close your curtains, though?
Different people have different preferences. I use roll-up shades and would not stand having a blindfold.
My sister prefers a blindfold and has only very airy light curtains in her bedroom, for aesthetics ...
Most hotel rooms have darkening curtains these days, but... I said "most": if you travel a lot, it may be good to be prepared. I have also seen people wear them on trains, to make it easier to sleep while travelling.
Not for me though: the only time when I have been able to sleep in a seat on a train, I had a cold.