Show HN: Belshazzar's Clock, luminous paint night clock
blog.karliner.net

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73 points

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mkarliner

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3 days ago

19 comments

Cerium ・ 3 days ago

Sweet hack, thanks for sharing. I remember playing in the dark with luminous paper as a kid - If I remember correctly, I would take a hacked up disposable camera and put various objects in front of the paper before triggering the flash.

I imagine that you could improve the consistency and readability some by modeling the state of each pixel of paper. That way when the drum comes around you can compensate the exposure per pixel based on the current state to achieve better uniformity of display. In this way you could do exposure compensation on each row of output to make the display equally bright top to bottom. This would be similar to how a "no-refresh" epaper display works.

  • mkarliner ・ 3 days ago

    Interesting, I'll have to think about that. Actually, with rare earth paints, the big issue is persistence, which is rather too long. In the current script, I only turn the drum 1/4 turn, so it takes roughly 4 minutes to illuminate the same patch again. Otherwise the lowest digit tends to be blurred because it is a combination of the last two values.

    • thanatos519 ・ 3 days ago

      Have you tried 360nm LED? The higher orbitals drop faster or so I've been told.

      • mkarliner ・ 3 days ago

        Another interesting suggestion to think about. Thanks.

    • avidiax ・ 2 days ago

      Maybe you could make a clock based on a cylinder of sealed powder. You draw the time on it, and when it's time to update, you rotate the cylinder enough to mix the exposed powder and draw the next time.

      Maybe the same thing could be done with beads and something similar to the marble machines to replenish a screen of beads, then dump it when the time is invalid.

  • xattt ・ 3 days ago

    > I would take a hacked up disposable camera

    Memories unlocked of extracting the flash unit from disposable cameras to flash on demand.

gigaflop ・ 3 days ago

Not sure if you can get this where you are, but I've personally used some of these glow powders, and they get very bright: https://unitednuclear.com/glowinthedark-items-c-101_45/

I've had Aqua and Green, and they look gorgeous.

  • mkarliner ・ 3 days ago

    Thanks, I'm in the UK, and US-UK shipping is horrendous, but I may give them a try.

    Right now I'm try to find a longer persistence photochromic for the daylight version.

    • bigiain ・ 2 days ago

      Have you come across Stuart Semple/ Culture Hustle?

      He makes a lot of interesting paints and pigments, and is UK based.

      https://culturehustle.com/collections/powder

      I've bought a couple of versions of his blackest black paint, and one of his whitest white, and they've all be extraordinarily good.

      I have some of his "LIT - THE WORLD'S GLOWIEST GLOW PIGMENT", but I haven't used it yet. I have no doubt it'll be great as well.

      (I have a vague plan to paint a motorcycle in Black4.0 to see if it's unreflective enough to evade the IR laser speed detectors cops use here...)

      • djsavvy ・ 2 days ago
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        That's a great idea. I'd love to see if it works.

        I've wondered whether it would be possible to design a motorcycle with a surface that's non-reflective to radar because of it's shape or texture, like how stealth planes work.

        EDIT: I realized the super black paint is probably the worst thing you could do for your own safety on a motorcycle, but that's besides the point...

        • bigiain ・ 2 days ago

          I've been riding motorcycles for about 30 years now, I started back when Neal Stephenson's Zodiac was still new, and this part was still ringing in my head:

          “I had to ride slow because I was taking my guerrilla route, the one I follow when I assume that everyone in a car is out to get me. My nighttime attitude is, anyone can run you down and get away with it. Why give some drunk the chance to plaster me against a car? That's why I don't even own a bike light, or one of those godawful reflective suits. Because if you've put yourself in a position where someone has to see you in order for you to be safe--to see you, and to give a fuck--you've already blown it... We had a nice ride through the darkness. On those bikes we were weak and vulnerable, but invisible, elusive, aware of everything within a two-block radius.” ― Neal Stephenson, Zodiac

        • exmadscientist ・ 2 days ago

          My brief experience with Black 4.0 was not particularly impressive. This video pretty much hits it dead on: https://www.youtube.com/watch?v=oKOC3Z9tDiI

          I didn't compare with the other paints (I only found that video after ordering the paint...) or with the difficulty of painting (I got the intern to do it!) but in terms of the final result, that's exactly the same result I got.

          I also have some of their glow pigment and it's a lot more impressive. This particular color doesn't glow very brightly or for terribly long, but the hue... glow pigment isn't supposed to be this color!

rob74 ・ 3 days ago

Looks cool, but if the "writing on the wall" is only supposed to be the current time, there are enough (much more mundane-looking of course) alternatives, e.g. https://www.walmart.com/ip/Emlimny-Digital-LED-Projection-Al...

  • Terretta ・ 3 days ago

    Indeed. And the red most use (a) doesn't blow your night vision, (b) isn't visible through your eyelids. (I recommend one where, if it also displays the time itself, shows the time in red too, at least when the room's dark.)

    Once you've had this on the ceiling for a while, it's annoying to have to look for time on a nightstand or your wrist.

froh ・ 2 days ago

fun :-)

say, why don't you move mirrors but the whole laser?