Having a tendency to shy away from social obligations and instead read on the Kindle for hours non-stop, I wanted to learn if the Kindle has blue light.

The Kindle Paperwhite emits a small amount of blue light. However, it is front-lit, directing light towards the screen not straight to our eyes. We can also reduce its intensity and there is a dark mode option to further reduce the amount of light reflected to our eyes.

The common reasons we are concerned about blue light are the possible effects it has on our eyes and sleeping patterns. Let’s begin with a summary of various blue light theories and their effects.

What is Blue Light and what is wrong with it?

If you are outdoors on a sunny day, you are practically bathing in blue light. This is because the sun is the biggest emitter of blue light on the planet. 

Exhibit A. Blue light in the sky. Photo by Gonard Fluit.
And a question: Why is the sky blue? (Answer at the end of this post).

Remember that light is a spectrum of colors, from red to green to blue to violet. Blue light is part of that spectrum. And each of these colors varies in the energy that they contain. With violet being the strongest, blue next.

So blue light is basically a part of the light spectrum that emits a higher amount of energy. 

Some blue light is beneficial. It boosts alertness, helps with memory functions, and elevates our mood. It signals to the body that it’s daytime, thereby regulating our circadian rhythm. The problem is when we get too much exposure and exposure well into the night.

Studies indicate that too much of these high-energy rays can lead to eyestrain, headaches, and blurry vision. It also interferes with our sleep cycle, causing us to have more difficulty falling asleep.

People also tend to blink less when reading. Which further increases the light shining to our eyes.

On the other hand, some studies like this and this, says blue light itself doesn’t adversely affect sleep. So it’s useful to keep a healthy skepticism before drawing any conclusions.

Nevertheless, it wouldn’t hurt to manage exposure to these light rays. And there are several ways to do so. More on that later. 

First let’s look at how much blue light the Kindle expends compared to other devices, including non-digital ones. We’ll use data from fluxometer.com.

Comparison between Kindle and other devices ¹

Device	Brightness compared to daylight in %	Phase shift in minutes
Kindle Paperwhite half brightness	0	0
Kindle Paperwhite full brightness	7	10
Galaxy S5 Active	25	40
iPad Mini Retina	28	45
Surface Pro 3	40	63
Nexus 7 Gen2	42	67
iPhone X	54	85
iPad Pro	61	96

Device	Blue light (weighted power) in µW/cm2
Kindle Paperwhite half brightness	0.122
Kindle Paperwhite full brightness	0.98
Galaxy S5 Active	2.58
iPad Mini Retina	3.7
Surface Pro 3	5.13
Nexus 7 Gen2	5.8
iPhone X	5.47
iPad Pro	10.1

The metrics displayed in the table are:

Brightness compared to daylight: Indicates how big an effect on your body clock as being outdoors in daylight. For example, if you see 25%, it means that if you spent 4 hours in front of the device; it has approximately the same effect on your body clock as spending 1 hour outdoors in daylight.

Phase shift: shows how much you can move your body clock in just one night if you see it for long enough (a few hours) typically before bed.

Blue light (weighted power): this is an estimation of irradiance in microwatts per square centimeter. Irradiance is the light energy (or power) received by a given surface.

All of these figures were taken using the default parameters in fluxometer.com. 

Please do not take these numbers as exact conclusions on how much blue light each device will produce. There are so many arbitrary factors that would affect blue light in your actual situation. Including distance, angle, light bouncing on the walls, etc. 

Rather, we can use these numbers and pay attention to their relative differences to each other. This way, we can have a reasonable estimate on the level of blue light that the Kindle emits compared to other devices.

Comparison between Kindle, common light bulbs and others ²

Light Source	Brightness compared to daylight in %	Phase shift in minutes
Full moon	0	0
Ordinary candle	0	0
Kindle Paperwhite half brightness	0	0
Kindle Paperwhite full brightness	7	10
Christmas tree	29	46
Philips Ambient LED	30	45
GE Incandescent bulb	35	55
LED 5000K	54	85
Philips TL950 fluorescent tubes	58	92

Light Source	Blue light (weighted power) in µW/cm2
Full moon	0.0131
Ordinary candle	0.0929
Kindle Paperwhite half brightness	0.122
Kindle Paperwhite full brightness	0.98
Christmas tree	1.71
Philips Ambient LED	2.13
GE Incandescent bulb	2.38
LED 5000K	5.71
Philips TL950 fluorescent tubes	6.64

Front lit vs back lit

This is one of the major differences of the Kindle Paperwhite compared to other devices. Instead of having LED bulbs shining from the back of the device pointing towards you, the bulbs are recessed along the sides pointing at the screen. 

In this way, it's closer to a reading lamp than the back lights of mobile devices. This results in much softer light reflecting to the eyes while keeping the screen properly illuminated. 

Options to reduce blue light being reflected to us

Still, despite the Kindle emitting much less blue light, and being front-lit, there are several ways we can reduce the blue light even further.

• Reduce the brightness of the front-light.
  You can do this by tapping on settings in the top menu. This also has the side benefit of reducing battery usage.
  
  
• Dark mode
  This option inverts the screen so that most of the display is dark and the text is white. This would reduce the amount of light reflecting towards you. 
  
  You’ll notice this clearly when you adjust the brightness level while in dark mode. Observe that there is less difference between brightness levels, because there’s much less white on the screen.

• Blue light blocking glasses
  Check out the reviews in Amazon.com and you’ll see many testimonials of how effective they are in alleviating eye strain (from reading on screens in general, not specifically the Kindle). And there are studies that back them up.
  
  However, note that there are also some studies like those mentioned earlier, that present a different conclusion. I suppose we’ll just have to see for ourselves what works for us.

• Blue light blocking screen stick-ons
  These are like screen protectors that you would have to stick on top of your device. Note that it's a rather permanent fixture. And you need to be very careful in applying it evenly to avoid “air bubbles”.
  
  
• Kindle blue shade
  This is only for the back-lit Kindle Fire tablet, not for the Kindle e-Ink devices. I only included it here to remove the confusion.
  
  
• 20-20-20 Rule
  A common guidance on preventing eye strain, the rule recommends looking at an object at least 20 feet away, every 20 minutes, for 20 seconds.
  
  
• Deep Breaths
  This is my favorite method. Not just to protect from excess blue light, but also to reduce eye and body strain in general. The challenge here is how to remember to take those breaths. For that, we can use a trigger. 
  

Breath Per Page

This has been tremendously helpful to me, I’d like to propose an acronym for it: BPP.
As in “Breath Per Page” or DBPP “Deep Breath Per Page.”

Often when busy, we only take shallow breaths and might even forget to breathe altogether! 

The idea is to train the body to close the eyes and take one full breath every time we turn a page. You’ll have to think about it at first, but after a while, it becomes automatic like muscle memory: Turn page -> Breathe. Turn page -> Breathe.

This method lends itself well to turning a page in the Kindle. Because you don’t have to think much about it. You know exactly where to position your eyes once you reopen them.

Deep breathing relaxes not just the eyes, but also the head, neck, shoulders and the entire body as well. This means we can go on reading longer without being tired. Before, I used to have very tired eyes after reading just for a few hours. Not anymore.³

Being less tired also means we can focus more. And although counterintuitive, it might even speed up our reading over-all. 

The duration of each breath depends on how much time you have. Deeper and longer breaths naturally lead to more relaxation. And something else too:

This method has had a remarkable effect on my comprehension. In those few seconds that my eyes are closed, I can almost see what I just read. I can see it being organized by my brain. As if “saving” it to my old cranky, hard drive.

As a result, I can follow the train of thought more efficiently. 

In summary, the Kindle does emit a small amount of blue light. But it’s much less than most digital devices, and even less than common light bulbs. 

Incidentally, if you are comparing the Kindle vs Paperbacks, you might need a stronger source of external lighting for the latter, which could actually expose you to more blue light on balance.

While it’s good to consider the effects of blue light on our sleeping patterns, I find that personally, my level of interest is what keeps me up at night. More than any blue light could.

Do you have other methods to take care of your eyes? I’d love to learn from you! Please let me know. 

P.S. Here’s the answer to Exhibit A, on why the sky is blue.

Resting the eyes from all these blue light. Photo credits: Bigbird3

TECHNICAL NOTES 

¹ Details about the instrument and measurement models can be found in the specific fluxometer page for each device.

² For light bulbs, no wattage was indicated as the readings were scaled to 100 lumens. So the readings can be interpreted as, "if you were exposed to 100 lux of this type of light, it would produce this much phase shift".

³ I’ve been experimenting on using this method for the computer as well. The trick is to use the Page Down key as much as I can, instead of scrolling with the mouse. And then train the body to take a breath every time I hit that key.

Incidentally, perhaps this is another plus point for the Kindle not being able to scroll.