Blue Light Exposure Calculator

Understanding Blue Light Exposure

Blue light is high-energy visible light with wavelengths between 380-500 nanometers. It is emitted by the sun (our largest source), LED lights, and digital screens. While blue light during the day is beneficial for alertness and mood, excessive exposure — especially from screens at night — can disrupt your circadian rhythm.

How Blue Light Affects Sleep

Blue light suppresses melatonin production more than any other wavelength. Melatonin is the hormone that signals your body to prepare for sleep. Using screens within 2 hours of bedtime can delay melatonin onset by up to 3 hours, making it harder to fall asleep and reducing sleep quality. Harvard researchers found that blue light exposure shifted circadian rhythms by twice as much as green light.

Screen Blue Light vs Sunlight

While screens emit far less blue light than the sun, the concern is about proximity, duration, and timing. We hold phones 20-30 cm from our eyes for hours, and we use screens after sunset when our bodies should be winding down. The sun provides about 100,000 lux, while a typical phone provides about 80-200 lux — but at close range and at biologically sensitive times.

Protection Methods

The most effective method is reducing screen time in the 2 hours before bed. Night mode features (iOS Night Shift, Android Night Light, Windows Night Light, f.lux) reduce blue light emission by shifting the display toward warmer tones. Blue light filtering glasses can reduce exposure by 20-60% depending on the lens coating. For daytime use, the 20-20-20 rule helps reduce eye strain regardless of blue light.

Blue Light Glasses: Worth It?

Research on blue light glasses is mixed. A 2021 Cochrane review found insufficient evidence that they reduce eye strain. However, many users report subjective improvement in comfort. Their primary benefit may be for evening screen use, where any reduction in blue light can support melatonin production. If you buy them, look for lenses that filter at least 30% of blue light in the 440-460nm range.

Recommendations by Age

Children's eyes transmit more blue light to the retina than adults, making screen limits especially important. The American Academy of Pediatrics recommends no screens for children under 18 months, limited use for ages 2-5, and consistent limits for older children. Adults should aim to stop screen use 1-2 hours before bedtime for optimal sleep quality.