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

[Cerium]

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]

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.

[xattt]

> I would take a hacked up disposable camera

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

[gigaflop]

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]

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.

[rob74]

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]

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.

[jareklupinski]

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

[mkarliner]

Very interesting challenge. May need a slightly different tech. Stay tuned :-)

[froh]

fun :-)

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