Blue light does seem to have effects on the brain. It can alter your circadian rhythm – your natural pattern of being awake and sleeping – though it’s not clear how. It might be by reducing your levels of a hormone called melatonin, or by exciting the SCN (which is like your brain’s clock). Blue light is natural, and probably helpful when we have it during daylight, but too much of it when we would naturally be going to sleep can be unhelpful – since smart phones are a major source of blue light in our lives, switching their screens’ blue light off probably does help! I’ve got a setting on my phone that switches it off after dark, and I quite like it 🙂 Not sure if it’s helped my sleep, but it certainly hasn’t hurt!
I won’t dispute the effects it has at all – I remember trying to sleep with an old fluorescent light on years ago that had a blue-ish tint, and it kept on waking me up because it felt like daylight. Despite the fact that I *know* it’s not a bright idea, I usually use my phone or kindle right before bed anyway. It doesn’t seem to affect me terribly – although I will struggle to sleep if I’m using my computer after 8 or 9 PM, but I’ve usually assumed that’s because my mind’s awake and thinking about the work – or gaming ;P – that I was doing.