The Definitive Guide to Blue Light

The Hidden Impact of Your Light Environment

We now spend almost 90% of our lives indoors. The repercussion of this: we are exposed to unnatural light sources that are confusing our biology.

This isn't just about blue light blocking glasses or turning on night mode on your phone. The relationship between light and human biology runs much deeper, affecting everything from your sleep quality to your metabolic health, hormone production, energy levels, and even your longevity.

Let's dive into the crucial differences between natural and artificial light, why your body responds so differently to each, and practical solutions that go beyond the typical "reduce screen time" advice you've heard before.

What is Blue Light?

Blue light is a band of color in the visible light spectrum, which makes up a small piece of the entire spectrum of electromagnetic radiation. The spectrum of visible light starts at the color Violet and works its way up to Red, in terms of elongating wavelengths... or in terms of frequency it starts at the color Red and makes its way up to Violet (wavelength and frequency are inversely related so higher frequency = shorter wavelength).

ROYGBIV - Red, Orange, Yellow, Green, Blue, Indigo, Violet (aka the colors of the rainbow) are the colors of the visible light spectrum. Visible in terms of what we can see as humans.

The "visible" spectrum runs from about 380nm of wavelength (violet) to 750nm (red), and the rainbow is everything in between. The 380nm wavelength of violet light refers to the length between one full wave cycle or distance from crest (peak) to crest of the electromagnetic wave.

The major differences between any form of visible light (and any electromagnetic wave in general) is the wavelength, frequency, and energy of the wave. All light, and all electromagnetic waves, are composed of photons. Photons have zero mass, but they have energy and momentum. These photons act as important input signals for our biology, and all life on our planet.

Blue light is typically defined as visible light that ranges from 450-495nm in wavelength. In terms of the visible spectrum, it is on the lower end of wavelength and thus on the higher end of frequency and energy. Only indigo/violet light has higher energy photons that we can see (ultraviolet or "UV" light is the highest energy wavelength of light that reaches our body from the sun—but we cannot see it).

This is important because the higher energy property of blue light is what defines how it uniquely drives specific biological functions in our body on a daily basis. Blue light wavelengths can be up to 60% higher energy than red light. This is why it is so "stimulating" to our biology.

Blue Light from the Sun vs Blue Light from Technology

Blue light from the sun is NOT the same as blue light from man-made sources such as screens or lights. Why is that? A few reasons:

• Blue light from the sun is never present without the rest of the visible + infrared light. It's part of a complete, balanced spectrum
• Blue light from screens are highly isolated in the wavelengths of light they use
• Blue light from screens + lights typically have a high amount of flicker

Blue Light from the Sun

The biggest difference between the blue wavelengths coming from the sun and the ones coming from screens or artificial lights, is that the sun provides a full spectrum of light alongside the blue.

The time of day and season will dictate how much ultraviolet (UV) light there is, but any time your body is exposed to sunlight you are not getting any blue light, UV, etc. in isolation—you are getting the entire ROYGBIV visible (VIS) spectrum + Infrared + UV. This matters because it means that sunlight is balanced.

High energy wavelengths such as blue, violet, and ultraviolet induce a larger oxidative response from our cells, which in excess can cause cellular damage.

Lower energy wavelengths, such as red and near-infrared are more restorative to our cells, with research showing that they can improve mitochondrial function and mitigate oxidative stress.

Near-infrared (NIR) light can even induce production of the potent anti-oxidant hormone melatonin at the sub-cellular level. These lower energy and longer wavelength light waves can penetrate inches deep into our biology.

The ratio (in optical watts) of NIR:VIS light that reaches the earth's surface is:

• 3:1 around sunrise/sunset
• 1:1 at high noon
• Zero: the amount of NIR in modern lighting/displays

Blue Light from Man-Made Sources

The sun is a "broad-band emitter". Conversely, blue light from our screens and lightbulbs are "narrow band emitters". This means they only emit a handful of wavelengths that are far different from the light spectrum of sunlight. Most technology screens and indoor light bulbs (LEDs, fluorescents) are very rich in the blue spectrum of light, have very little red light, and are completely absent of infrared light.

This is both a bi-product of aesthetics and the need to meet energy efficiency standards in regards to light bulbs. While sunlight balances blue light with restorative red+infrared, modern screens and lighting do not.

Incandescent and halogen bulbs are far more rich in the red/infrared spectrum but because of that characteristic are thus "energy inefficient" and have subsequently been banned for sale. The DOE (Department of Energy) is seemingly unaware that the infrared light causing the "energy efficiency" is actually incredibly important for our biology.

As you can see in the light spectrum plot above, the light in a standard cool white LED has a high amount of blue light, almost no red, and zero infrared. Because the blue light in displays and lights are not balanced with red+infrared, it can be concluded that they are far more likely to cause oxidative stress at the cellular level. This has been shown in various studies looking at isolated blue light and its effect on our biology, specifically in damaging cells in the retina.

Flickering Blue Light

The last major difference between sunlight and "man-made light" is the way it reaches our eyes. Sunlight is and always will be a continuous stream of photons. Man-made light, LEDs specifically, are almost never continuous. They are highly pulsed, or "flicker", by design.

LEDs are actually being switched ON and OFF at rates too fast for our eyes to visually perceive (but not too fast for our brains to notice) in order to control their brightness. This electronics control mechanism is called "Pulse Width Modulation" or PWM. It has become the industry standard because it allows for more precise signal control and color consistency, especially at low brightness levels.

Some well-documented side effects of flickering LEDs are:

• Eye strain, headaches, migraines
• Aggravation of autism symptoms
• Photo epilepsy
• Anxiety

This is likely a large reason why a large percentage of adults suffer from digital eye strain, and often feel very fatigued at the end of the work day.

Blue Light's Important Role in Our Biology

Blue light is not all bad, and is extremely important for us to sustain optimal health. The main role of blue light in our biology is to set our internal body clock or circadian (24-hour) rhythm. Like any system, our body runs on a certain time scale, and in order to function optimally the system needs to be in synchronicity from a timing perspective. There are many signals that drive our circadian rhythm, but the dominant input that drives our body clock is light. Blue light specifically is the master "zeit-geber" or "time-giver". Blue light is nature's stimulant, and thus is especially important to be exposed to in the morning and mid-day hours.

Our mammalian biology has evolved over millions of years using these mechanisms, and the light environment that dictates our circadian rhythm (and thus optimal biological function) is sunlight. The blue light from broad spectrum sunlight tells our body what time it is, providing wakefulness and guiding cortisol secretion when we are first exposed to it in the morning. Then at night time, when the sun is down, the absence of light (especially blue light) signals the body to begin to produce the sleep-inducing hormone melatonin. We are meant to be in sync with nature's rhythms.

Your Circadian Rhythm and Chronic Disease Risk: What's the Connection?

Blue light, in the wrong context, can have quite a negative impact on our health. When we go against nature's rhythms on a consistent basis, we are unfortunately causing havoc for our biology.

Blue light at nighttime will disrupt our circadian rhythm and suppress melatonin (3 to 4 times greater compared to lower energy wavelengths like yellow/orange/red). This occurs because blue light is meant to be the master time setter, and at night time is when we are most sensitive to higher energy wavelengths. Sleep is the foundation for optimal health because it is when our body goes through restorative processes such as:

• Autophagy (cell recycling)
• Apoptosis (programmed cell death)

A dysfunctional circadian rhythm is problematic because if the timing for our biological systems is off, we have chaos at the cellular level and are not able to repair cellular damage as effectively. This is why circadian disruption has been linked to nearly all chronic diseases, including:

• Cardiovascular disease
• Cancer
• Infertility
• Neurological diseases

It may seem far less tangible, but your light environment is seemingly more important for optimal health than we could have ever imagined.

The World's First Blue Light Free Computer

If we spent the vast majority of our time outside, like our ancestors did, we would never have to worry about our light environment or circadian rhythms being disrupted. However, we live in a modern world (thankfully), and the progression of society has shifted us to an indoor dwelling species. According to the EPA, we now spend roughly almost 90% of our time indoors. Our jobs and devices tie us to this indoor world, keeping us away from the bright full spectrum sunlight during the day. Simultaneously, we are exposed to far too much light at night—staring at our devices late into the evening hours.

Our mission at Daylight is to enable the reversal of this trend. We wanted technology that allows people to have brighter days and calmer nights, which is in line with our natural rhythm. That is why we built the world's first blue light free computer, that can also be easily used outside.

The DC-1's LivePaper™ display technology is reflective, so it can be seen even better in direct sunlight. Unlike emissive displays, it has an incredibly long battery life (20-60hrs) and does not overheat as easily either. For night time use, we built a custom LED spectrum backlight that can be 100% blue light free, so that you don't have to worry about disrupting your sleep or circadian rhythm to a high degree if you are looking at a screen before bed. The DC-1 solves some of the key issues as to why technology can be disruptive to our health, at the root cause level.

Our backlight uses custom amber LEDs to provide a blue light free solution at the hardware level. This is a more effective way to reduce blue light exposure at night because it addresses the issue at the root cause: the light emission from the LEDs themselves. Most "night modes" in modern devices do not filter out all of the blue light, unfortunately.

For those who are blue light savvy and use software screen light filters, you know that they are an imperfect solution as well. In order to remove all of the blue light from a software perspective, you have to go to "full red mode", which ultimately leaves you with a very narrow band of red light and poor user experience. This is due to the fact that our photoreceptors in our eyes are far less sensitive to red light. As a result, you have to crank up the brightness just to see anything!

The plot below illustrates a study that found light at night with a brightness 5 times higher (2500 lux) resulted in a melatonin concentration that was about 30% lower than the control (500 lux).

Our amber backlight has a broad spectrum of light, so you can mitigate sleep disruption while still having an enjoyable user experience. The warm amber hues can be seen at very low brightness due to the purposeful inclusion of a small amount of green + yellow wavelengths.

As seen in the plot above, our night time vision (scotopic) peaks in sensitivity around 510nm (green) light and has almost no sensitivity to red light.

More similar to a candle or campfire (both have a tiny amount of green light), the DC-1 backlight appears far brighter than a "full red mode" iPhone at the same luminance.

Building technology with circadian principles and your health in mind.

How to Improve Your Light Environment

When it comes to optimizing our light environment, all we are trying to do is copy what exists in nature. Blue light is not bad when it comes from sunlight, but problems do arise when we are looking at unbalanced blue dominant screens all day long in infrared deficient indoor environments. Our eyes, brains, and overall health is suffering as a result of our poor light environment, and it quite simply does not need to be that way.

Here are our favorite ways to improve your light environment & circadian rhythm:

Daytime 🌞 Get Outside as Much as Possible!

• Be a weekend warrior - a CU Boulder study found that one weekend camping can fully re-set your circadian rhythm
• Go for walks throughout the day
• Eat lunch outside (weather permitting)
• Watch the sunrise! Getting full spectrum light in your eyes first thing in the morning is extremely beneficial for setting your rhythm for the rest of the day

Indoors 🏠 Optimize Your Environment

• Use infrared-rich incandescent or halogen bulbs to improve your indoor light environment
• Work in a room with more natural light
• Open windows (weather permitting)

Nigthtime 🌙 Protect Your Eyes at Night

• Watch the sunset and begin winding down your day
• Dim your light environment as much as possible at night time
• Our favorite cozy nigthtime lights are incandescents and beeswax candles
• Use a Daylight Computer for at night screen time
• Use blue light blocking glasses (ones with at least yellow or amber lenses)
• Enable software screen light filters

Final Thoughts: The Journey to Better Light

Our understanding of light's impact on human health is continuously evolving. What's clear is that the light environment we are exposed to has profound effects on our wellbeing, energy levels, and long-term health outcomes.

At Daylight, we're committed to ongoing research and development of solutions that bridge the gap between modern technology and our biological needs. Our first device is just the beginning of our mission to help people live in better harmony with their natural circadian rhythms.

Take a moment today to assess your light environment. Small changes—getting morning sunlight, reducing evening blue light exposure, or using technology designed with your biology in mind—can make significant differences in how you feel and function.