Researchers have been saying for years and years that reading an on LCD screen late at night will disrupt your sleep, and techies have been working nearly as long to come up with fixes for that problem.
There are two general solutions to the problem (three, if you count not using your device within two hours of going to bed). One is called a night reading mode, and the other is using the software settings to apply a blue light filter to the screen.
One common solution offered by many reading apps is to invert the colors so that the text is white on a black background. It's called a night reading mode, and you can find it in most reading apps such as Kindle, iBooks, Aldiko, Kobo, etc, and looks something like this:
The night reading mode is not unpopular with ebookophiles, but I'm not sure that it really counts as a solution to the sleep problem.
Anecdotal reports suggest that it might help (some users swear by it) but the only true solution would be to use a blue light filter.
Study after study has shown that the blue light emitted from a screen can impact your sleeping patterns. Why blue and not any other color? I don't know the answer to that, but I can say that it's what everyone is saying and it is where all the app developers are turning their attention.
If you like to read or work on your PC late at night then you should look at an app called f.lux. It adjusts the color settings on your monitor based on the local time for your location.
And most importantly, it changes the color settings on a system level. So if you install F.lux, it will affect all the apps you use and make them look different.
The F.lux app for Windows comes so highly recommended that I've not heard of an alternative. But I can't make the same remark about Android.
Kindle Fire Tablets
In December 2015 Amazon released an update to Fire OS Bellini which added a blue light filter called Blue Shade.
Update April 2019: That feature is still included on all current models, and you can see screenshots here.
In the four years since I first published this post Kobo has made blue-light filters a standard feature on all their ereader models, including the Kobo Forma. Turn the feature on, and the white frontlight on a Kobo will slowly shift to orange and then a reddish tint as your evening progresses.
You can also set the Kobo's blue-light filter manually, but I do think it's worth mentioning that no testing has been done on the frontlight of an ereader to see whether said frontlight has the same negative impact as an LCD screen.
Nope, the Kindle does not have this feature, and Amazon has shown no interest in adding it.
I am expecting a new premium Kindle model in 2019, however, and that would be a good time to add it.
A quick search of Google Play reveals that there are countless free apps which claim to offer a blue light filter, but I'm not so sure how true that is. I've checked a half-dozen, and many simply turn down the backlight and apply a grey, and not blue, filter. There are a few apps which do apply a color filter, and some even offer alternate color options for the filter (here's one).
One app in particular, Twilight, has been recommended several times in the comment section of this post. I'd try that first. Also, Google added a blue light filter to Google Play Books in late December 2015.
When I first wrote this post in 2015, we had far fewer options for late night reading on your iPad or iPhone. Google updated the Google Play Books iOS app, and Opera, for example, updated their browser with a night reading mode and a blue light filter, but there's no general solution. There's also night reading mode in ebook apps, I only found a few options for iOS.
But then Apple added this as a core feature for iOS, which means you have the option with all iOS apps. See the "Night Shift" menu under "Display and Brightness" on your iDevice's Settings menu for more info.
Not having other devices to check, I can't tell you whether you can find blue light filters on other platforms.
If you use one, let us know in the comments. I'm sure I won't be the only one who is interested.