[Michael Karliner]’s Belshazzar, named for the Biblical character upon whose wall the writing appeared, is a unique light painting machine, that tracks an array of UV LEDs across a glow-in-the-dark background to paint transient dot-matrix letters in light. It was one of many cyberpunk-themed art pieces in Null Sector at the 2018 Electromagnetic Field hacker camp this summer.
The row of LEDs hangs down from a carriage that traverses a tubular rail, and is edged forward by means of a stepper motor driving a roller. This arrangement delivers the benefit that it can be scaled for displays of any length. The LEDs are driven from an Arduino via a Texas Instruments TLC5940 PWM driver ship.The result can be seen in the video below the break, and those who saw it at EMF may remember it tracing suitably dystopian phrases.
The higher dynamic range of the Mk1 Human Eyeball means that the display is rather more effective in RL than on video.
To the extent that the full line of text was visible when the write was finished.
Yep, that’s a (very) old video and done with auto exposure, so the display is better in real life.
An interesting area to explore for longer target material light emission could be the conjunction of formulation and fabrication methods, such as adding variety of secondary fluorescence chemicals (spectral cascade issue with implicit colour change) and mix of range of sizes of crystalline nano particles as well as overall thickness of course Eg for longer light path length and maybe even some lithium niobate type dopants, given that material’s strange properties…
I’d love to hear more on yourideas for material improvements. Actually, a real issue was the persistence being too long, as the next message started being written before the last was fully gone. A later version of Belshazzar ran on powered tracks and was designed to run around long continuous tracks to obviate this problem, but proved too unwieldy and unreliable for installation.
I like the motorized aspect! I did a hand feed style one a few years back (using processing, fade candy and some neopixels with a .jpg source image) https://www.flickr.com/photos/andrewsharmon/14232474535 .
( Still picture from the interlaced 2 row one https://www.flickr.com/photos/andrewsharmon/14045820398/in/photostream/ , with greyscale!)
Brilliant, thought provoking thanks for that :-)
Curious what is the average period of persistence before say the image degrades by a just noticeable amount like 10-20% ?
Is there a trade name/product id for the sheet in your link ?
Actually, that one just used cheapo, toy store glow in the dark paint. The later one at emfcamp used https://www.glowtec.co.uk/paint-usage.htm
If you flash the image on quickly it all fades down pretty evenly. I’m not positive on the persistence curve of that material, but I think it was rated to glow for a long time.
For that one I used the glow sheet that sparkfun used to sell. But I have since found that there are some nice glow vinyls available in large sheets ( 5′ x 5′ for automotive wrapping applications) on amazon (kinda expensive though)!
That’s very nice. What leds did you use?
Those were some WS2812 LEDs that I just used the blue channel on. Though I think I recently saw Adafruit started selling ws2812 LEDs with UV die inside.
Actually, this is the original version (1) of Belshazzar. The one at emf (version 4) was re-engineered to be able to run for three days solid reliably. It also used an on board Raspberry Pi to do the rasterisations and had an MQTT connection to take new messages. Version 2 of Belshazzar used a UV laser to do vector drawings and version 3 (failed) ran wirelessly on powered tracks so it could go round and round a continuous track and leave continuous messages behind it.
The inside of a dark shipping container at night was the perfect environment for this. Not only was it clearly legible there were the faint ghosts of whatever came before in multiple layers.
The group Floating Points had a similar effect for their live show when I saw them last summer except they used a laser with beam splitting, looked excellent and complimented the music perfectly.
https://www.youtube.com/watch?v=rftHUlBgh7I
Again, looks far more impressive through the human eye.