This is one of those goofy products that you didn't know existed but are glad they do.  I read in bed every night before turning out the light, and it's hard to hold the book open with one hand. (The other is used to hold the magnifying glass.)  I wished for a solution, but didn't know what form it would take.  Then I saw these and ordered them and voila! - problem solved.  A very helpful bit of plastic.