Get rid of Kindle Paperwhite's backlight

[joblack]

Originally Posted by HarryT

I'm absolutely fine with calling it a sidelight, if that's what floats your boat. Just (please!) don't call it a backlight .

I'm happy with every direction as long is it is disabled.

[ProDigit]

Originally Posted by HarryT

I'm absolutely fine with calling it a sidelight, if that's what floats your boat. Just (please!) don't call it a backlight .

We could call it a back-side light?

[geekmaster]

Originally Posted by joblack

Exactly but the light originates from the side. So it's a sidelight.

It is a sidelight only when it is in landscape mode. In the default portrait mode it would be a bottom light, as ixtab said.

But the light guide surface layer redirects that light source inward onto the eink layer, from the front. So technically, the eink is frontlighted from a redirected bottom light source.

[HarryT]

Yes, the lower part of the picture I posted clearly shows this.

[DrSnuggles]

I've a question.
Is it a result of the jailbreak that the kindle even has light on if the cover is closed (screen saver picture is shown).
Even if I press off button and screen goes white, the light is on.

or is this normal?

[HarryT]

This is a known bug which is fixed in firmware version 5.3.1. Are you using an older firmware version? Reboot the PW to make the light go out.

[DrSnuggles]

It's 5.3.1. I get the Kindle with 5.3.0, made the update to 5.3.1 and then jailbreaked it.

Reboot has fixed it, but when get's the bug triggered?

[ProDigit]

Is there a way to, say, switch between off (0) to on (10), instead of current settings?

I'll never going to use above light setting 10, so is it possible to just darken the overall light settings?

Even at 1 it's still light enough for me (like not too bright, but still I wished I had one more darker setting for reading in the pitch black).

[DuckieTigger]

Originally Posted by ProDigit

Is there a way to, say, switch between off (0) to on (10), instead of current settings?

I'll never going to use above light setting 10, so is it possible to just darken the overall light settings?

Even at 1 it's still light enough for me (like not too bright, but still I wished I had one more darker setting for reading in the pitch black).

No you can't get any lower light (other than off). This is how the lightlevels of the light slider on screen correspond to the level of the actual device:

level 0 - device 1        level 10 - device  13       level 20 - device 147  
level 1 - device 2        level 11 - device  19       level 21 - device 170 
level 2 - device 3        level 12 - device  26       level 22 - device 196 
level 3 - device 4        level 13 - device  36       level 23 - device 224 
level 4 - device 5        level 14 - device  47       level 24 - device 254 
level 5 - device 6        level 15 - device  60         
level 6 - device 7        level 16 - device  75 
level 7 - device 8        level 17 - device  90 
level 8 - device 9        level 18 - device 107 
level 9 - device 10       level 19 - device 126

As you can see up until level 10 it goes in small steps. No wonder Amazon does not list any battery life time for light higher set than 10 (if the numbers for the intensity are any indicator for powerusage). Plus as you can also see, it gets larger fast - theory of me is the logarithmic scale of light - to make a bright light visibly brighter takes a lot of juice.

I have also worked out a way to turn the light off. It already works on my PW - every time my PW wakes up and the light is set to the lowest level (no bar on screen) it turns the light completely off, but only once on wake up (no messing with the crontab file). If I go to the light setting and turn the light up, it will turn back on, even if the slider is set back to 0 - it will stay on the lowest light. To turn it off again it is necessary to put device back to sleep and wake it up. To make it even more convenient, there is a file that needs to be put on the usb partition to enable the turning off of the light. So it can simply be renamed or deleted if the automatic turning off is not desired. Put it back and it turns back off next time you wake the PW up.

Now I only have to pack it into an update_*_install.bin so that it can be used even on PW's that don't have USB Network installed.

[ProDigit]

it would be cool if you could re-rout that 'off' setting to a number (say level 24, if you're not using it much).

Have you tried changing one of the level values to 'device 0' or '-1'?
If it would work, the system would send a negative voltage to the leds, which only allow current flow to flow in the positive direction, so they should block the light.

Just suggesting..

Also noteable, that the kindle does the light in 8 bits, or 256 intensities. So far they only use 254 on yours. Perhaps you can get it to work brighter than the stock settings by modifying the values!

[DuckieTigger]

Originally Posted by ProDigit

it would be cool if you could re-rout that 'off' setting to a number (say level 24, if you're not using it much).

Have you tried changing one of the level values to 'device 0' or '-1'?
If it would work, the system would send a negative voltage to the leds, which only allow current flow to flow in the positive direction, so they should block the light.

Just suggesting..

Also noteable, that the kindle does the light in 8 bits, or 256 intensities. So far they only use 254 on yours. Perhaps you can get it to work brighter than the stock settings by modifying the values!

Blocking the light, very funny. It complains if you try sending a negative number - well not complain, but cap it beetween 0 and 255. If you send one too big it goes to 255. and the difference from 254 to 255 is not even visible.

And yes, the way to turn the light of is by changing the number to 0. Just like on the first page of this thread. I don't think it will be a good idea to use a different light level for the trigger to turn off on wakeup.* It is a cosmetic reason first, as the screen will turn on and flicker right off. I tried it on level 24 and it was pretty annoying. The other reason not to make it customizable is user-error. Right now it just checks if a file is there or not, but I don't intend to check for every possible mistake you can make by having to configure it inside that file. It also goes hand in hand with other things on the Kindle like USE_ALT_FONTS - same basic principle.

*It would not be a problem, it checks the lightlevel right now to make sure that it only activates at level 0.

[ProDigit]

sorry, was at work, attention was not 100% with my writing.
I meant 'block power', as LEDs only allow a current one way.


So you could make the file something like this then, and it would turn off at level 0?:

level 0 - device 0        level 10 - device  11       level 20 - device 147  
level 1 - device 1        level 11 - device  17       level 21 - device 170 
level 2 - device 2        level 12 - device  25       level 22 - device 195 
level 3 - device 3        level 13 - device  35       level 23 - device 225 
level 4 - device 4        level 14 - device  47       level 24 - device 255 
level 5 - device 5        level 15 - device  60         
level 6 - device 6        level 16 - device  75 
level 7 - device 7        level 17 - device  89 
level 8 - device 8        level 18 - device 105 
level 9 - device 9        level 19 - device 125

[geekmaster]

Originally Posted by ProDigit

... Have you tried changing one of the level values to 'device 0' or '-1'?
If it would work, the system would send a negative voltage to the leds, which only allow current flow to flow in the positive direction, so they should block the light. ...

Not negative voltage, but negative time, because the LEDs are controlled with PWM (Pulse Width Modulation). How do you propose sending them a negative pulse width (where the pulse ends before it begins)? Current understanding of physics would require a moving wormhole to accomplish that.

Because modern white LEDs are really blue LEDs with a white phosphor coating (similar to fluorescent lights), varying the voltage would not work as expected. Even colored LEDs are much more efficient with PWM control than by varying their voltage. Also, LEDs can self-destruct with a reverse voltage applied to them (as little as a few volts in some cases, but 5V reverse breakdown is typical).

EDIT: As I posted about three months ago, value zero does turn the paperwhite screen illumination completely off:
https://www.mobileread.com/forums/sho...d.php?t=193068

How could reverse-biasing the LEDs make them even darker than applying NO voltage at all?

[ProDigit]

Their forward voltage is 3V, their backwards voltage could sometimes range in the tens of Volts.
I'm sure that the sub 3,6V is not going to harm them.
Besides if it was voltage oriented, and the kindle had 2 x 3,6V batteries, the '-1' would be only a 1/256th of 7,2V, or 0.03V, which would not harm the leds.

If it is like you say, digital (which you're probably correct), then value '0' could mean always on, or always off (I mean, it is a possibility that the timer set to zero, might actually keep the voltage regulator in it's previous state, which might be 'on').

More than likely it'll be off though...

[geekmaster]

Originally Posted by ProDigit

Their forward voltage is 3V, their backwards voltage could sometimes range in the tens of Volts.
I'm sure that the sub 3,6V is not going to harm them.
Besides if it was voltage oriented, and the kindle had 2 x 3,6V batteries, the '-1' would be only a 1/256th of 7,2V, or 0.03V, which would not harm the leds.

If it is like you say, digital (which you're probably correct), then value '0' could mean always on, or always off (I mean, it is a possibility that the timer set to zero, might actually keep the voltage regulator in it's previous state, which might be 'on').

More than likely it'll be off though...

As was posted earlier in this thread (more than once), I posted the values and their brightness levels back in October. The slider sets a maximum value of 254 and a minimum value of 1, but from a script or command line you can set 255 or 0 (which is completely off).

As mentioned previously, most common LEDs have a MAXIMUM reverse breakdown voltage of 5V. Exceeding that value can destroy them.

The kindles may contain voltage converters, so you cannot safely assume that all voltages in the device are less than the battery voltage. Anyway, it does not make sense to dedicate a DAC (especially a bipolar DAC that would require positive AND negative supply voltages) to controlling the LEDs when it makes no sense to reverse bias them.