Anecdotally: I look at a computer screen a lot, well into the night, and noticed that I found it often hard to go to sleep. Looking into this, I learnt that computer screens and phones have a high colour temperature, strongly blue-biased, which led me to suspect it was messing with my day/night sense. i happened upon a program called f-lux which allows you to alter the temperature and program it to alter with your 'day', such that the colour warms up as you enter evening. it seems to have done the trick and I don't get insomnia as often now. The colour of the light affects melatonin. I don't think it's voodoo.