All, yes, all these devices have a luminous screen. Nice for using indoors or on an overcast day outdoors, but in sunlight these screens are hardly readable. And, using such a device with a starcharting app on it kills your night vision, unless you wrap it in 1 oe 2 layers of red foil.
And late at night the harsh white light contains too much blue light which impairs our sleep, unless you use F.lux/Nightshift/CF.lumen kile apps which do not work on all devices.
Sincs the mid-00s there exists a
transreflective screen which was used on e.g. the Nokia E70 and Nokia N810, which were well readable in bright sunlight, although the colors were not vivid.
And development on the e-ink displays (for ebooks) is also on a standstill as color and fast response e-inks are not available yet.
The industry rather increases the number of pixels to a whopping 2560x1440 on a 5" screen, better than most HD TV's, making them even more power guzzling. Normal eye can hardly discern the difference between 1280x720 and 2560x1440 on such small screens, while the processor has to control 4 times the pixel count. And they rather make the displays more and more luminous in daylight to beat against the sunlight.
Obviously, all these fancy things boost up battery usage and cancel out the lower power processor to 'save' battery power. It seems that research to alternative lower power displays has no priority because of Samsung et al. make lots of money with the luminous screens. Like the oil industry is slowing down development of renewable energy.
If there were a tablet available which only lights up in the dark (and even then can be switched off to use a red flashlight when using as a star atlas) and even less resolution and the battery has twice the life I'd be the first to buy such a device.
