openmoko at mazikeen.demon.co.uk
Thu May 21 12:37:35 CEST 2009
On Thursday 21 May 2009, zogg wrote:
> Thats intresting. What could have stopped them from making it
> non-monochrome in daylight?
Probably cost and efficiency as these were major factors in OLPC. If PixelQi
don't start producing screens that are colour in daylight then I guess there's
a technical reason as well. Based on the explanation below I would have
thought adding the coloured filters between the LCD and the reflective layer
would drop backlight efficiency only a little since the prism has already
split the light, but I'm no expert. The extra component requiring precision
placement would add cost though.
> Tim Schmidt wrote:
> > On Thu, May 21, 2009 at 9:12 AM, zogg <zoggified at gmail.com> wrote:
> >> Looks like LCD for indoors are common, and for outdoors theres scarcity.
> >> So, do you know any manufacturers, or at least in what direction should
> >> i try and look at?
> > The OLPC has an LCD which is very easy to read in daylight. When
> > backlit, it appears as a color LCD, but when frontlit (as from the
> > sun), it appears greyscale. This is a function of the OLPC's very
> > efficient backlight system (instead of using colored filters to block
> > out 66% of the light from the white backlight for each pixel, they use
> > a fresnel prism to split the backlight into it's component wavelengths
> > on pixel boundaries. Thereby allowing nearly 100% of the light
> > produced by the backlight through to your eyes, as opposed to less
> > than 33% for typical LCDs. Light from the front of the LCD passes
> > through the pixels, and is reflected by a silvered layer, back through
> > the pixels to your eyes, never passing through the prism, so what
> > would normally be colored sub-pixels appear as greyscale pixels.
> > --tim
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