Ask HN: Can we make a computer screen light in color when turned off?

https://news.ycombinator.com/item?id=41581303

by hypertexthero • 2 years ago

3 13 2 years ago

news.ycombinator.com

Or is keeping displays on all the time the only alternative to black rectangles?

ezekg• 2 years ago

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).

solardev4• 2 years ago

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)

hypertexthero4• 2 years ago

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.

solardev4• 2 years ago

Your typical e-ink screen will be white when turned off. I think transflective LCDs too, or alternative display techs like https://daylightcomputer.com/

You can get monitors using those technologies if you don't want it to be black when off.

theGeatZhopa2• 2 years ago

Didn't search for it, but there was a young man (backed by his parents) who regularly got eye irritation while staring at a screen. So that guy just pulled the backlight and started to sell it on the webz as eye friendly screen. Guess, didn't start off like a rocket. It's been one or two years ago here on hackernews.

hypertexthero4• 2 years ago

Thanks for the detailed reply.

I imagine a black back on the screen improves contrast when it is on, as well.

Guess I’ll throw a nice colored cloth over the screen when it is off for now :)

hypertexthero4• 2 years ago

I remember those silver-gray displays in old calculators fondly, and love the word “transflective”!

Thanks for the Daylight Computer link!

solardev4• 2 years ago

I didn't come up with the word transflective BTW. It's just what the industry calls them, and you can actually buy them from niche vendors.

theGeatZhopa2• 2 years ago

There's one problem and that's how our eyes work. They need photons to enter them to be able to see. The photons are being "reemitted" by the body we look at. The body absorbs the light shining on it and just reemitting the photons that aren't absorbed by the body's surface. So, actually, what we perceive as color are photons that haven't been absorbed by the body.

Black screen means it absorbs everything. Because it's a translucent body consisting of a few layers, the light simply gets trapped within the layers and is not reemitted into our eyes. We perceive that as black.

If you want to make it whatever color, you need a not translucent screen, so the photons are partly absorbed and partly reemitted. Then we have some photons in our eyes and sensations that can be interpreted by our brain as information/color/whatever.

The screens of e-ink utilize that. But they're slow.

So to answer your question, no it's not possible to make ordinary screens to have a color, except there's a solid body in front of the layers to absorb and reemitt the photons.

To build a screen like that, one would need a backlight. No matter where it comes from. Or, inverted LCD on a white plane that alters the refraction when there's a current flowing. That would consume more energy because all the pixels need to be constantly powered (and after powering off, they would automatically alter their refraction..)

So, no..

What about constantly low powered screens like Samsung's the frame?

brudgers• 2 years ago

With the right set of engineering requirements, yes. But typical engineering requirements preclude it because typically opposed features are more important for a display.

And for some use cases, placing a sheet of white paper over the display might be good enough. Good luck.

codingdave• 2 years ago

If you just want a different aesthetic when your system is powered down, you don't need to change the screen itself - just drape a piece of cloth over it.

Ask HN: Can we make a computer screen light in color when turned off?

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