Blue Light Melatonin Delay Calculator
Enter how much screen time you get in the two hours before bed and how bright your screen usually is. Get an estimate of how much your melatonin release might be delayed, and what that means for your effective bedtime. Nothing uploaded.
Results
Rough estimate based on general sleep-science findings about blue light and melatonin suppression - individual sensitivity varies considerably. Informational only, not medical advice. Discuss persistent sleep issues with a doctor.
Learn more: Blue light suppression and sleep timing
How blue light delays melatonin release
Blue light wavelengths (400-500 nm) trigger special photoreceptor cells in your eyes that suppress melatonin production. When you use a bright screen in the 2 hours before bed, your brain receives a signal that it is still daytime, delaying melatonin release by 10-90 minutes depending on brightness and exposure duration. For example, 1.5 hours of high-brightness screen time can shift your melatonin peak roughly 21 minutes later, making it harder to fall asleep at your planned bedtime.
Brightness matters more than you think
Screen brightness is the primary lever. Low brightness (night mode or dimmed) multiplies the effect by 0.6x, medium brightness by 1x, and maximum brightness by 1.4x. The relationship is non-linear: doubling screen time does not double the delay, because melatonin suppression plateaus. Individual sensitivity varies significantly based on age, sleep history, genetics, and light exposure throughout the day - this calculator provides a rough estimate, not a medical prediction.
FAQ
Does blue light blocking (glasses/filters) actually work?
Blue light blocking lenses and screen filters reduce the 450-470 nm wavelengths that most strongly suppress melatonin. Research shows modest effects - roughly 20-30% reduction in suppression. They are worth trying if you must use screens late, but sleep hygiene (stopping 1-2 hours earlier) is more powerful.
What if I need 2+ hours of screen time before bed?
This calculator caps the relevant exposure window at 2 hours because most melatonin suppression research focuses on evening light exposure in that window. If you use screens longer, the delay estimate plateaus. Your best option is to stop screen use 1-2 hours before your target sleep time, or use the lowest brightness setting available.
Does reading on paper vs a screen make a difference?
Yes - paper books under typical room lighting have negligible melatonin suppression because they emit no light and reflect ambient wavelengths evenly. Screens emit blue light directly into your eyes. Even dim screens suppress melatonin more than reading by lamplight.