The reason blue light hurts is purely biological. Sleep is a part of the circadian rhythm, which is the cycle of biological processes that are determined in part by the levels of light and dark exposed to our bodies.

In the most natural setting, which is one where we’re only exposed to sunlight, our retinas sense when the sun descends and the environment grows darker. That induces our hypothalamus to start the process of producing melatonin and other sleep hormones and reducing our body temperature.

When we use artificial lighting to extend our day, however, our bodies get confused and the various sleep signals are disrupted. Even worse is the blue light emitted by fluorescent and LED lights — like those on our various device displays — which cause us to be more alert and produce even less melatonin.

That’s why using a blue light filter is so important.