Quote:
Originally Posted by mike.s
Actually, it might be possible. With LEDs, brightness is almost always controlled using PWM, varying the ratio of on/off. Frequently, it's implemented at a fixed frequency, where when the on time increases, the off time decreases.
White LED color output can vary somewhat when one compares short "on" times with longer ones. That's because the color changes for different currents, and it takes a finite time to turn the LED on or off. So even though the "full on" current stays the same, the average current for each on cycle varies slightly.
So, if one instead does PWM by keeping the on time constant and only changing the off time (and hence the frequency), a more consistent color can be achieved across all levels of brightness. You just need to ensure that the frequency is kept high enough to avoid perceptible flicker. There are other factors which would still cause a bit of color shift (such as LED temperature), but current is the main influence.
I have no idea if the PW hardware supports that, or if newer software does that, but it's not impossible. |
That is some interesting stuff. If somehow the leds and the controller are capable of creating different color-temperature of white, that would work. If it can be adjusted by software alone, than it might even work with software update alone. Right now the leds are pretty much the same color ( a bluish tint). Since the eink background is pretty much warm colored (yellowish) the screen appears whiter with higher lightlevel. It could simply be the blue light finally outblasting the yellow background. The way to compensate for that should be to have the leds not the same color, but more blue at low level, and warmer at high level. That could make the screen appear at the same color temperature, but only different intensity. But all that would only work if the color temperature of the leds in the PW can be changed with software alone.