Projects/Reflective backscreen

Idea of a reflective backscreen

Hi, I was referred to this page to give feedback concerning an idea for the development of the upcoming OLPC X0. The idea struck me,as OLPC has somewhat immitated Nintendo Gameboy SP with a TFT screen on a reflective background.

The materials used for the reflective background usually are white transparent plastic, with on the back a LED light or mini-TL (tube Light). I thought of using a shiny metallic backplate, but that would negate any screen backlight.

So my second idea was to use the technology of a reflector of a bike, motorbike or a car. the reflector itself reflects the light back in the same direction as where it came from. But modifying the plastic triangle (pyramid) structure on the back of a reflector, one can actually capture light from a wide angle and concentrate it on a narrow space (the user's viewing area).

By directly reflecting not only light that comes straight unto the screen, but also light that comes from an angle, I think it should be possible to create a device that will not need any backlight at all, and the device possibly has a better contrast ratio then the standard OLPC/original gameboy (1994)-like screens. eg: light that originally would enter the screen at a 160 degrees angle, could be captured, and send in an angle between eg: 120 and 60 degrees. another possible positive thing could be that leds can be used as a lightsource, shining possibly through the reflectors (or the new reflectors can be created with holes to support LED's to be build in. Light emitted from those LEDs could be reflected back (focused) in the user's face.

Positive points

• No more backlight needed in daytime
• cheap to manufacture,light in weight, and durable
• Especially functional in outside (sunny) environments like Africa
• Technology relies on older TFT/LCD technology, and needs no new software or hardware

Possible drawbacks

• certain parts of the screen could be lighter (brightness) then other parts
• coloration issues could appear due to bending light in a prism (rainbow colors like on a CD's surface, or prism could appear)
• Technology could need a sort of polarization filter
• There would be no way to adjust backlight brightness other than changing display brightness (turning pixels darker).
• display can be hard to create to give satisfying light reflection in low light as well as in full sunlight environments (Dynamic range) (Long exposure to direct sunlight or bright light might cause stare; while a too low light reflection might make the screen unreadable.
• Using a gameboy like system to darken the contrast ratio can or may result in lesser contrast ratio,or colors. I'm not expecting to get more then 8 bit (256 tint greyscale) out of a reflecting technology; perhaps 13 to 16-bit (4.000 to 16.000) colors max.

Other options

Another option could be OLED technology which is more expensive to manufacture, but requires less energy than standard LCD. As far as I know OLED/AMOLED can not be paired with a reflective backscreen since their technology is vastly different from LCD/TFT.

Study should be done in to define what technology is more battery efficient;(AM)OLED technology or (TFT)LCD technology without background light. Obviously the AMOLED will work greater in dark places, indoors, and in places outdoors that are not exposed to full sunlight. The reflective TFT screens are used best in light environments like in full sunshine,or a well lit room; while when being LED backlit can also be used in darker places, despite using more energy than the OLED.

A 8-bit greyscale standard screen can also be easily created, using pixels with the technology of an electric calculator screen,and a reflective or light (white) background. At a cheap price (sub $100 laptop) the device will not only be interesting for poorer people, but for hackers and software/hardware modding as well