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Redscale raster display

For nocturnal and other dark uses
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As mentioned elsewhere, the planetarium programme Stellarium has a “night mode” to prevent dazzle when observing the real night sky. This is basically red. Remarkably though, other than Nixie tubes and LEDs, displays tend to be reluctant to invade this end of the visual spectrum unless they also use other colours.

My suggestion is that a display be made which only shows colours at the red end of the spectrum, in a fairly novel but also quite low-tech way, which is only visible to the dark-adapted eye. Uses could be as follows: darkrooms (not terribly useful nowadays), watching videos in the dark when one wishes not to disturb sleeping partners, children or simply wants to fall asleep more easily, observing the night sky without being dazzled, spying on people without being detected, alarm clocks, night time radio and media player displays and watching nocturnal animals without disturbing them. It appears at first sight to have two other advantages: low energy use and low “technology” use.

The human eye can become very sensitive to light if in complete darkness. A commonly-quoted example is that vision can allegedly detect a candle flame from twenty kilometres. Provided an object emits enough light, it can be visible at a size well under one minute of arc in the visual field, for example stars, all of whose apparent diameters are below a second of arc by many orders of magnitude.

They are also good examples of dim light sources. A sixth magnitude star has a luminosity of ten nanolumens per square metre, whereas Venus, the brightest object in the night sky other than the Moon, is around a seventh of a millilumen per square metre. These are really, really dim lights, but all easily visible to the human eye under the right conditions. Most of them cannot be clearly perceived to be of a particular colour due to the poor function of cone cells under such conditions, and the resolution of the eye is also low due to the way rod cells are connected up to the optic nerve.

The display consists of a rectangular grid of pixels. Each pixel is a very small helical strand of wire like a filament bulb, less than a hundred microns long, offering a standardised degree of resistance, behind a convex lens to reduce the gaps which would otherwise exist, in an inert or evacuated atmosphere, each one being discrete and replaceable. Different light levels vary continuously from off up to the magnitude of Venus. The light is generated by heating the pixel with the electric current until it is red hot, but only of a sufficient temperature to give off enough photons to appear as bright as somewhere between a faint star and Venus. Damage is avoided by the helical shape, just as with a light filament. Colour temperature would vary but at such low light conditions this would probably not be visible so much as colour as something akin to a non-linear variation in luminosity, which could be taken into consideration.

The whole display is fairly low resolution by the standards of a computer monitor because visual acuity would in any case be lower in darkness. Changes in light level on the display would need to take into account the relatively long persistence of the pixels and the possibility of expansion and contraction causing the pixels to fail. Hence the frame rate of videos would have to be slower than normal. Text displays, rather than scrolling, should change in a page-flipping style, or with an input buffer at the bottom of the display.

nineteenthly, Dec 31 2010

Inspiration Programming_20Under_20the_20Stars
Thanks, [Vernon] [nineteenthly, Dec 31 2010]

Stellarium http://grok.lsu.edu...spx?articleid=12345
"Night mode" mentioned near the bottom of the page - makes it red. [nineteenthly, Dec 31 2010]


       I may be failing to see things clearly, but what is wrong with a red filter over the screen of a standard display?
MaxwellBuchanan, Dec 31 2010

       It would have to be either a very dim display or an almost completely opaque filter, the resolution would be wasted, it would use unnecessary power and it would be made of substances difficult to obtain. This could be made from any solid metal, drawn into a wire, cut into slices and placed in an evacuated chamber under a sheet of convex lenses. It's a video display attainable with late nineteenth century technology or earlier.
nineteenthly, Dec 31 2010

       Are you suggesting that a red-only filter is particularly challenging to produce? Come to that, how difficult can it be to get an unfiltered monitor to display in red only?
MaxwellBuchanan, Jan 01 2011

       [nineteenthly] Do you remember the monochrome amber display for the BBC computer?
spidermother, Jan 01 2011

       You have to remember that i've been expecting the collapse of civilisation ever since i watched 'Survivors' thirty-odd years ago, so these things are always on my mind. I started off thinking about Stellarium, but i now think this would be more useful for watching telly late at night without disturbing one's spouse, and i also think this is something you could sort of bang together from scrap. So, in the post-apocalyptic nightmare that will ensue after giant pandas take over the world or something, we can sit in our bunkers in almost complete darkness with our vinegar-beercan-nail and pedal-powered portable DVD players watching old Doctor Who videos on heating element redscale monitors while the vicious bamboo-eating cuddly toys try to break through our boarded-up entrances while our significant others get a good night's sleep.
nineteenthly, Jan 01 2011

       Oh, sorry, amber monitor! Yes. I also have a laptop with an orange plasma display. It's a bit too bright though.
nineteenthly, Jan 01 2011

       This is basically a large, high resolution, red dot matrix vacuum fluorescent display. Futaba (or one of the other manufacturers, but their specialty is custom high-res displays) could probably make one for you, but it would not be cheap.
Spacecoyote, Jan 01 2011

       Interesting, thanks. Could maybe be stuck together?
nineteenthly, Jan 01 2011

       Producing red light by heat is horribly inefficient. Most of the radiant energy is in the infrared. Think of the dim light produced by a 2,000W bar radiator, which is barely enough to read by.   

       An array of LEDs, in contrast, would be far more efficient than any display available today, and would be doable, especially as you are willing to accept a lowish resolution and monochrome. If you were willing to accept an orangey red, the power needed would be even less, as the eye is more sensitive to such wavelengths.
spidermother, Jan 02 2011

       I agree that it's inefficient when it's a large heating element and you're trying to use its reflected light, but this is for direct viewing in almost complete darkness and the elements are microscopic when they aren't glowing. You could be right because i haven't done the calculations but i suspect this is possible. And orange is fine because this would probably not be perceptible to colour vision.   

       Making an LED is far from a trivial task, as far as i know, involving doping and highly pure elements with low abundance.   

       Having said that, a sufficiently dim array of LEDs would not suffer from the fact that it would be low-res because the eye is low-res at that light level.
nineteenthly, Jan 02 2011

       //orange is fine// No it isn't. Deep red is used because it doesn't affect night-vision components (specifically rhodopsin in the rods)
FlyingToaster, Jan 02 2011

       True, now you come to mention it, but that just makes it use less energy so no problem.
nineteenthly, Jan 02 2011


       If you add a fan you could speed up the refresh rate.   

       Either way, it'll be popular for winter nights in the observatory.
FlyingToaster, Jan 02 2011

       I have to do lots of maths now.
nineteenthly, Jan 02 2011

       Really its not low tech if you count that the computer its hooked up to (and is useless without) is a product of advanced technology and manufacturing.
Spacecoyote, Jan 03 2011

       It doesn't follow that it's linked to a computer and i haven't specified the kind of computer. This could be seen as a big panel of blinkenlights.
nineteenthly, Jan 03 2011

       This makes me want to go doublecheck my toaster for low-res messages from Venus through the coils. And football updates don't need nearly that much bandwidth.
RayfordSteele, Jan 03 2011


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