On my computer I use an app called f.lux that alters the shading of my screen depending on the time of day. I can’t exaggerate how important this app has become for me — it seems so minor but it’s changed my life. I literally sleep better because I’m not seeing the harsh blue glare in the evening. http://justgetflux.com/
PLEASE allow developers to have this kind of control over the screen on iOS devices. I’m seriously considering jailbreaking my devices just for this one app — and if you knew me you’d understand that I REALLY hate the idea of jailbreaking. I would love to see it in the App Store, and they say they’d love to make it — but Apple doesn’t allow it.