Illuminated Artwork: Star Atlas

How I made a wall-hanging illuminated artwork titled Star Atlas. I have described how the wooden enclosure was made in another Instructable.

The germ of this piece was industrial junk: specifically the LCD shutters I harvested from a burned out video projector. These have a very fine-pitch grid of transparent pixels which act like a diffraction grating that gives anything viewed through them a spectral fringe. I wanted to experiment with the perceptual effect on interior lights in a box.

Because the shutters give a very regular fringing effect, I wanted a less predictable arrangement of interior lights. I've always been intrigued by how the ancients (and the more recents!) saw amazing patterns in the unstructured pattern of the stars. So here was an idea: start with star constellations.

I was influenced by John Cage, noted for his random compositions, as well as Joseph Cornell who famously put constellation charts in boxes. While I could have used any number of star charts, I used the note position from the Cage composition Atlas Eclipticalis, which in turn was based on star charts. To do this, I converted one page of his manuscript found at the New York Public Library into a dxf of star positions using Inkscape. I imported this into EagleCad, and carefully placed a tiny surface-mount LED on top of each star position (musical note).

This circuit was very straightforward: a number of white LEDs in parallel, with individual current limiting resistors. I used 603 surface-mount white LEDs and 805 resistors. I fabricated the board on the Othermill, it went very quickly. To get the long aspect ratio I laid out the circuit in two halves on a 4 x 5 piece of single-sided copper board, then bandsawed them apart and soldered them together end-to-end. (Note the schematic is a little misleading: the two LEDs on the ends are not used, I just use the footprint as a convenient header pattern for the wires from the battery.)

Stars come in different colors and widely different apparent brightness. I would have liked to find the apparent magnitudes from the original star charts Cage used for his manuscript but I will leave that to a future musicologist-astronomer.

I varied the brightness by using larger and smaller resistors to vary the current through the LEDs, and I used different brands of LEDs to mix up the color a little. (Different white LEDs have different phosphors with slightly different colors that vary from yellowish to bluish.)

In order to be truly random I used a method similar to that which John Cage used to compose music: the I Ching divination method, where I tossed a trio of coins to select between LED colors (yellower or bluer) and brightnesses. To vary the brightness I used three different dropping resistors of 100, 330, and 1K: these are roughly a factor of three apart because your eye perceives brightness logarithmically rather than linearly.

I was hoping the 603 LEDs would be small enough to look like stellar point sources; unfortunately they weren't. Early experiments showed the rectangular LED housing was quite visible. In order to get a more point-like illumination I made a star mask with pinholes at each star position. This was easily done from the EagleCad: I exported the layer with the LED center positions as a DXF then used a laser cutter to make tiny holes at the center of each LED. I attached this over the circuit board with double-sided tape. To make sure I aligned it properly I attached it with the LEDs lit up: it was very satisfying to precisely align the holes with the lights :)

The front panel was made from 1/8 inch black acrylic. I wanted the LCD "windows" to be flush with the front, so with some experimentation I found I could use the laser cutter to remove enough material from the back around the hole for each window such that they could sit almost perfectly flush. This makes for a satisfyingly crisp appearance. Once the front panel was complete it slid nicely into the slots cut in the box for it, and I attached the windows by pressing them into the holes cut for them and securing them with aluminum foil tape which is both lightproof, permanently adhesive (unlike duct tape!) and easy to peel off should the need arise.

The back panel was 1/8 inch birch plywood cut with a laser cutter, with holes for the rocker switch and dimmer pot as well as the 4 6-32 screws that attach it to the wooden box, and two additional holes for the hanging wire. I sanded off the laser burns from the panel then went over it all with 600 grit sandpaper for a smooth finish.

Because the human eye is so sensitive to light, I wanted to make sure I could match the brightness of the artwork to the ambient illumination. If the work is too bright it would be annoying, or if too dim it would not be visible. So I added a 5K dimmer potentiometer in series with the battery. Because the LEDs are quite efficient it was possible to power the artwork from batteries: this is especially helpful when hanging it in galleries like the Pier 9 studio without distracting power cables (or having to pull them through the walls). I also added an on/off rocker switch so the work could be turned off to save batteries.