Really no point in comparing LCD technology with Eink. The screens are different and display different. If you are worried about eyestrain there is more literature out there talking about how bad the direct light of an LCD screen is for the eyes than an the indirect light of a frontlit Eink screen (which you can turn off or near enough).
Yes, I know that the technologies are different - I own both the devices and have posted comparisons in the past:
These were taken under bright sunlit conditions which favors e-ink, and the iPad Air is now quite an old model which lacked the high contrast, laminated, True Tone display of the newer devices (making it look blue-tinted here).
While it is true that you can (nearly) turn off the light with e-ink devices, I find that the display is duller than even a cheap paperback book when you do this, and can be difficult to read unless you are in good lighting conditions. I never found them comfortable to read with only a dimmed bedside lamp illuminating the display - particularly the older models before the Paperwhite.
They are
great if you are mostly reading in well-lit conditions; under a lamp, by a window, outdoors, or using its own lighting during the day where its blue tint is not an issue, but I do most of my reading last thing at night now, and find the iPad display preferable to it - particularly with red-on-black text.
As I said though: I'm not suggesting buying an iPad instead of a Kindle - the images were to demonstrate how the Kindle is lacking now for reading at night with its cool/blue lighting, and why I now prefer the iPad despite being LCD-based rather than e-ink.
Competing e-readers have offered warm lighting options or the ability to select a color temperature for a while now; Amazon is falling behind.
The jury is still out on the effects of blue light, by the way.
There is debate over the effects of near-UV blue light causing eye strain and leading to macular degeneration.
There's no debate about blue light interfering with melatonin production and affecting sleep.
That's why I spent quite a bit of money on lighting so that my lights can turn warm at night, and red for an hour before I go to sleep (in addition to having stopped using the Kindle). I now have a 120 day streak of this regulating my sleep cycle so that I can fall asleep at a specific time, when I've never been able to keep a consistent sleep pattern for more than a few weeks in the previous 10-15 years.
Eink is a stable display, there is no rapid refresh which some people believe causes eyestrain. The pixels also work differently so even a higher res LCD doesn't look the same as a lower res Eink. Eink is in modules that do not have spaces between pixels, LCDs do even if they are smaller than ever.
Yes, that's true - and it's one of the nice things about e-ink's monochrome displays. You can see it in the images I posted above, and this is an older (lower resolution) Kindle 4 for comparison:
The text looks somewhat pixelated, but is significantly more comfortable to read than an older "non-retina" LCD display.
I generally don't find eye strain to be a problem on high quality LCD displays though: meaning a high contrast IPS-type LCD that doesn't change much with viewing angle, and has "retina" quality resolution.
Only cheap LCD devices use PWM-controlled backlights that can result in eyestrain. Ironically the Hue lights that I installed ~4 months ago
do use PWM to control the color and dimming of the lamps, but I haven't found it to be much of an issue beyond noticing the stroboscopic effects of motion when they are dimmed low. PWM dimming is more of an issue for watching video on displays, in my experience.
And you absolutely can email more than book to your Kindle at a time. I just did it yesterday. Most 3rd party stores that sell Kindle compatible books make sending books to Kindle easy. Humble Bundle has you enter the devices email address, let's you check off the books you want, and send them all at once. StoryBundle is the same. But considering how tech savvy most of us on ResetEra are, using a program to convert eBooks isn't asking much.
Ah, I didn't know you could email more than one book at a time now. I normally download the books to my library, and then transfer them via Calibre.
It's not that it is
difficult to do this, it's that it is annoying having to manage a separate library for books on my Kindle vs all my other devices - particularly since I don't use my Kindle that much any more.
On an iPad I can just open up another app or access a book from my cloud storage instead of having to convert it and send it to the Kindle. It's why those Android-based e-readers from Onyx are more appealing to me than another Kindle - or would be, if not for the high price.
If Amazon were to add a warm backlight option, and could access Android apps, I'd probably consider upgrading. As it is, my Kindle is just sitting there not being used, and none of my family wants it either because they can't rent library books (with Overdrive being restricted to the US on Kindle for some reason).