Quote:
Originally Posted by John.Dorrian
Thus, LEDs with an emission peak of around 470–480 nm should be preferred to LEDs that have an emission peak below 450 nm...
|
One has to keep in mind that for LCD (and OLED) monitors one can set the color temperature of the display, it is user configurable in their menus so it is not correct to rely on the native color temperature of the illuminating LEDs which may have a lot of blue so of very high color temperature (maybe 9,000-9,500K? I haven't checked though). Typically monitors come from the manufacturer with the temperature set as "normal" at 6,500K or there about, so around the same as overcast daylight. Tablets (Android), as far as I know, do not normally provide for natively adjusting color temperature but applications may do so or else provide provision to do so.
I just now did some tests measuring some color temperatures (photographers will be familiar with all this, and I have played around doing this before for reading applications). First, as a check, I measured the temperature of overcast daylight; the result 6,500K as expected.
I then measured the default setting of 2 LED lit LCD computer monitor panels, both were 6,500K approx. I then measured the tablet I currently read on (Samsung TAB A 10.5, current model) at native temperature, it was 6,400K so a little warmer.
I then measured the color temperature with a book open in the Pocketbook reading app with the background color setting of Hex F4E4D4 (Red 245 Green 228 Blue 212) which on my tablet is a very slight sandy tint; it measured as 5,200K so that is much warmer than daylight, or the tablet's default native display temperature, and of the illuminating LEDs. [EDIT: using Wein's law at 5,200K the maximum height of the spectrum curve is around 575nm, so back in the yellow region]
Then in Pocketbook I set the background color to white (so Hex FFFFFF or R255 G255 B255) and the color temperature measured the same as the tablet's display native temperature of 6,400K. Effectively then, one has complete control over color temperature.
For reasons I have never gone into in both Pocketbook and Moon+ Reader the actual rendition of the color depends on brightness, so if one goes to
http://www.psyclops.com/tools/rgb/ and enters the above RGB values it renders a color close to bisque on a monitor, whereas on my tablet it renders much paler than that at the low brightness levels suitable for reading.
The outcome, for LCD is it is pointless to talk about LED wavelength and temperature - the panel temperature is a user setting on monitors and within the better reading apps on tablets (and phones) (and TVs too). I think for most people setting up background color for reading will find that the moment they get away from a pure white background they will be hitting the blue down in comparison to green and red so heading towards warmer temperatures.
That because I think most people prefer warmer lighting, in rooms typically around 3,500K (often called "warm white"), and if one has used a cool white compact fluoro, for example, (around 6,500K) as a room light they can be harsh and uncomfortable. Using a reflective reading medium such as a paper book I suspect most people prefer reading in a warm white lit room light (tungsten or the little cooler compact fluoro "warm white") than a "cool white" compact fluoro lit one.
The above means that if one is going to conduct an "reading comfort" experiment with subjects reading from various devices then the devices have to be set up correctly for reading with a good reading app, not just using the device's native settings for display temperature, brightness, etc.