“Blue light from screens destroys your sleep”

## The Evidence Blue light in the 450–490nm range does suppress melatonin secretion via intrinsically photosensitive retinal ganglion cells (ipRGCs). This is real and well-established from lab studies using isolated blue light at high intensity. However, a 2019 RCT by van der Lely et al. (later replicated by Chellappa et al.) found that blue-light-blocking amber glasses improved sleep in heavy smartphone users at night — but effect sizes were modest (10–15 minutes of sleep onset). A 2021 study by Mouland et al. in *Current Biology* showed that the colour of light matters much less than its brightness and the time of exposure. Dimming screens has a larger effect than blocking blue specifically. ## What's Often Overlooked The content you consume before bed — news, social media, work email — triggers cortisol and cognitive arousal that probably disrupts sleep more than the photons themselves. Both mechanisms are real; but "put the phone down" beats "buy blue-light glasses."