Quote:
Originally Posted by Jason90
Don't they tune each led to output the same amount of light before they lay them on top of the eink display,with every ereader being the same size and with the leds all being positioned in the same spots i still don't understand why this happens.
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Let's assume these are true. There's still a third element here: the transparent layer over the e-ink screen that all this light is being shunted through. And because of the nature of the material, to get even light, you depend on refraction/diffraction to bend the light as it passes through. And optics winds up being all about trade offs. You can't get a "perfect material" really, and so you have all this work to control sharpness, reduce false color, etc. And since Amazon is doing a sort of microscopic etching of the material to redirect the light, the tolerances are probably incredibly tight (if the source I've read is accurate that the etching isn't even a pattern, but changes as the distance from the LEDs grow).
Quote:
Originally Posted by Jason90
Unless they don't check the leds until they have been placed inside the final product and then say do a QC on every 1 in 100 or something and realise they need to check the leds again.
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It is impossible to test every unit that comes off the line without it being a non-trivial cost. Mass production has relied on statistical sampling within batches for decades. So yeah, if you have something with tight tolerances that has to be made cheap, it's actually surprisingly easy to wind up outside those tolerances. But this assumes we know what those tolerances actually are.
Quote:
Originally Posted by tomsem
My conclusion is that the tolerances involved are too narrow to control perfectly. It is probably the capacitative layer between the glass (or plastic) light guide and the e-ink layer that is responsible for the prism-ing, as it is sprayed on and very thin, so even a small variation in thickness can cause 'special effects'.
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It's possible.