I don't know why we don't see more LED-illuminated LCD displays where the backlighting, or whatever scheme is used, is available with a pushbutton. Many cellphones, just as one example, waste a relative lot of energy backlighting by presenting black text or image on a white background, when white (or some other color) on black, might work just as well. If that's efficient, then lots of equipment could be improved with the same strategy. Printers, some test equpment, etc, could benefit greatly from some sort of lighting on their LCD displays.

My HP network color laser printer has a flashlight fastened to it so I can read the display when necessary. A moderate LED array, costing less than a US dollar, including the driver circuit, would have improved the situation greatly. I've had dozens of HP and Okidata laser printers, and none of them had an illuminated display. Next time I need a color laser printer, it probably won't be an HP ... or an OkiData.

Given that ability, however, I can't imagine why anyone, anywhere, ever would use 7-segment LED's, except in a onesie or prototype, since there's so much inexpensive LCD glass with a 7-segment display.

I understand why one would do that with a scrolling display, or an alphanumeric display for varying lighting conditions, or requiring a wider viewing angle ... but why don't we see more 7-segment lcd's with multiple backplanes? They'd be easier to manage, and certainly less demanding on timing.

RE