Could work. I don't know enough about the specifics of experiment design for sleep research. You could also try things like transparent masks + lies ("they filter specific wavelengths"), etc. Studying people is awfully hard. Lying is generally allowed as long as you do the right things as far as advance ethics review and design (and usually informing the person later, etc.).
To be fair, the problem you are bringing up is larger than just sleep research. https://examine.com/summaries/study/0AKk3d/ is an interesting study that was looking at what is often thought of as a much more active drug.
My question is ultimately on whether that is a flaw in this study, or more to study? :D I'm probably placing too much weight on the word "flaw?"
