In my experience the iPad & iPhone cannot approach the dim levels side-lit eInk readers can. The minimum brightness on iPad/iPhone is about 50% of max on my K

In my experience the iPad & iPhone cannot approach the dim levels side-lit eInk readers can. The minimum brightness on iPad/iPhone is about 50% of max on my Kindle Oasis, so it might be hard to do a realistic study comparing the two, one or both of the devices would end up far out of the normal range users would select in order to match brightness. If I'm reading in a darkened room on my kindle I have the brightness on the kindle set lower than it's possible to do so on an iPhone or iPad. I think this is common, which shows how crazy it is the study had an iPad on maximum brightness and had the user read for hours in that configuration. I'd have red eyes and a splitting headache by the end of that which would of course have negatively effected my sleep.