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Comment by ezekg | Hacker News Reader

I mean, the absence of light is darkness, and light requires energy. That's why screens are black when they're off -- there's no energy source. The alternative would be constant energy drain for no reason, or something like e-ink (but that's expensive and afaik incapable of producing color).

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Not all displays default to blackness when there's no power... just think of a pocket calculator or old-school black and white LCD watch, for example.

(And also, there are color e-ink devices in the wild now, like https://us.kobobooks.com/products/kobo-libra-colour or https://remarkable.com/store/remarkable-paper/pro)

Thanks for the links!

I’d love a display that let me pick the color or picture showing on the screen when it is off, or maybe it’s the wrong question and power-efficient things with solar panels directing sun energy to batteries that keep them going on all the time is the way.

My black and white Kobo displays a book cover when it's asleep (with eink, the display doesn't use any power unless it's redrawing, so once a picture is up there, it stays there even if the battery dies). But I don't know what the color ones do, like if they let you choose a background color or if there are even color ebooks yet. Presumably you could make your own color ebook with Calibre and set that as your background cover, but I haven't tried it.

To make them go white, they actually have to use power to clear the image. If you just let it sit there and let the battery die, the image will be there until you recharge it and turn it back on.

E ink is really cool tech (just patented and expensive). But the daylight computer from the other comment might be more what you're looking for.

And yeah you can totally run a solar setup. Anker makes a bunch, for example, of portable li ion batteries that can be directly connected to their solar panels.

Edit: If what you want is a digital billboard or picture frame, there might be some of those out there too, or I think I saw some DIY projects building those out of eink panels and an Arduino or such. Some of them get commercialized on Kickstarter.

Thanks for the info and ideas! I’ll look these up.

I’m excited for the future with solar, battery, and really most electronic technology becoming cheaper and simpler.

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