When people struggle to fall asleep, the first assumption is stress or anxiety. Sometimes that is true. But for a large proportion of people who lie awake for 30, 45, or 60 minutes before sleep comes, the problem is simpler and more physical: the body has not been given the signal it needs to begin the sleep process.
The Signal Your Body Is Waiting For
Sleep onset requires melatonin, and melatonin requires darkness. The pineal gland begins producing melatonin in response to the absence of light - specifically the absence of blue-spectrum light, which your photoreceptors interpret as daylight regardless of the source.
In a natural environment, darkness begins at sunset. In a modern home, the lights go off when you decide to go to bed. The gap between those two events - often two to four hours - is where the problem lives.
Two Hours Is the Critical Window
Harvard researchers found that bright light exposure in the two hours before sleep is sufficient to delay melatonin onset significantly. Not just screens - overhead lighting, lamps, and even streetlight coming through curtains can be enough to suppress the signal during this window.
The practical implication is that what you do in the two hours before bed matters more than what you do in bed. Getting into a dark room and picking up your phone is not restful preparation - your brain is still in a lit environment as far as its biology is concerned.
The Simplest Fix
Dimming lights progressively in the evening helps. Removing screens helps more. But the most complete solution is also the most practical: a sleep mask that eliminates light entirely at the moment you want sleep to begin. Rather than trying to engineer your whole environment, you remove the signal at the point of reception.