from Hacker News

Show HN: Belshazzar's Clock, luminous paint night clock

by mkarliner on 1/8/25, 11:14 AM with 17 comments

• by Cerium on 1/8/25, 4:13 PM

  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.

• by gigaflop on 1/8/25, 4:33 PM

  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.

• by rob74 on 1/8/25, 4:18 PM

  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...

• by jareklupinski on 1/9/25, 1:25 AM

  i want to mix this with https://github.com/LingDong-/shan-shui-inf to make a real-life infinitely scrolling procedural animation

• by froh on 1/8/25, 9:11 PM

  fun :-)

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