Everyone tells you to stop using screens before bed. Few people tell you exactly when. And almost nobody explains why the timing matters as much as it does.
The answer is not arbitrary. It comes from a specific biological window that your body opens every night, whether you protect it or not.
What your body is doing 2 hours before sleep
Around 2 hours before your natural sleep time, a coordinated series of biological shifts begins. Your core body temperature starts to drop. Cortisol, the hormone that keeps you alert and responsive, begins to fall. And melatonin, the hormone that tells every cell in your body that night has arrived, starts to rise.
Your body is not waiting for you to decide it is bedtime. It is already preparing, running a hormonal sequence that sets the conditions for deep, restorative sleep. Interfere with this window, and you do not just delay sleep onset. You compress its quality.
Dim light melatonin onset: your body's sleep countdown
Scientists call this dim light melatonin onset, or DLMO. It is one of the most reliable markers of your circadian phase, and it typically occurs approximately 2 hours before your habitual sleep time.
Research by Gooley et al. (2011), published in the Journal of Clinical Endocrinology and Metabolism, found that exposure to room light before bedtime suppressed melatonin onset in participants by up to 90 minutes. That is not a marginal effect. It is the difference between your body preparing for sleep on schedule and your body staying in daytime mode well into the night.
DLMO is not fixed. It shifts based on the light signals your eyes receive. Bright artificial light during this window tells your SCN (your brain's master circadian clock) that it is still daytime, pushing your melatonin onset later and with it, every biological event that follows.
What artificial light does to this window
When you use a screen, check your phone, or sit under overhead lighting during your body's 2-hour preparation window, you are sending your circadian clock a false signal.
The result cascades through your night. Melatonin rises late. Core temperature stays elevated longer. Cortisol does not fall on schedule. Growth hormone, which is released primarily during the first deep sleep cycle, is delayed or diminished. The restorative work your body performs every night gets pushed into a compressed window, or missed entirely.
This is why sleep quality matters as much as sleep quantity. You can spend 8 hours in bed and wake feeling unrested if your circadian window was disrupted before you ever closed your eyes.
To understand the full mechanism behind why light controls sleep, read: Why Your Phone Is Keeping You Awake (Even When You're Exhausted)
The 2-hour protocol
The practical answer to how long before bed you should stop using screens is this: begin protecting the 2-hour window before your natural sleep time.
For most people this means starting around 9pm if you sleep at 11pm, or 8:30pm if you sleep at 10:30pm. The specific time matters less than the consistency. Your circadian system is a timing mechanism. Give it reliable signals and it responds with reliable sleep.
The challenge is that modern evenings happen on screens. Work, family, entertainment, winding down: all of it takes place in front of devices that emit melatonin-suppressing light. The protocol is not about removing screens from your evening. It is about reducing the biological cost of using them.
How Night+ supports the protocol
Our Night+ lens is built for exactly this window. Worn 2 hours before bed, it filters 99.9% of blue light and over 97% of melatonin-suppressing green wavelengths up to 600nm, independent spectrometer verified.
This means you can continue using your devices during the evening without sending your brain a full daylight signal. Your melatonin can begin rising on schedule. Your cortisol can fall. The biological preparation for sleep that your body wants to begin can actually begin, while your evening continues as normal.
You do not need to change your evening. You need to change the light.
To understand why most blue light lenses do not fully address this problem, read: Blue Light Glasses: Do They Actually Work for Sleep?
Two hours. Every night. It adds up.
Your body allocates 2 hours every night to preparing for the most important biological maintenance it performs. When artificial light disrupts that window, the effects accumulate: in your energy, your mood, your hormones, and your long-term resilience.
Night+ is designed for those 2 hours. The science says they matter. Your biology already knew.