lighting help for alertness when reading

when I read history books in my slightly dim room during day that don’t require a ton of concentration, I tend to get sleepy (I sleep enough).. I noticed that if I read on ipad in darkish room with a ton of brightness, I tend to stay quite alert.. what should I do? get a light therapy lamp? or a bright desk lamp?

thankyou very much for suggestions!!

PS: (I don’t have issue to same extent when learning math or some complex philosophical text, that require lots of very active thinking)