Construction

My lightboard is described here. Visit Lightboards of the World to check out the design choices of others.


As you read below, for part names shown in red, see more details on the Parts page. You will find a typical bill of materials there too.

Glass


The lightboard is a 4x8 foot sheet of heat-tempered PPG Starphire architectural glass, 10.0mm thick (also called 3/8 inch). The glass is lit internally from the upper and lower edges by bright white LEDs. Light travels to all parts of the glass by total internal reflection (TIR).


Getting unmarred glass can be a problem. See Build or Buy. And no, it can't be plastic. See FAQ.


Ordinary plate glass looks dark green from the edge. Because of the dark tint, not much light from the edge can reach the center of a panel of ordinary glass. Starphire glass has very low iron content so it is very clear. It looks pale blue from the edge. As a demonstration of how clear Starphire glass is, I shined a laser pointer in from the edge. You can see the beam bouncing up and back through the glass, reflecting from the inside surfaces by TIR, all the way across the panel:

I draw with fluorescent markers on the glass. The marks glow brightly due to their illumination via frustrated total internal reflection (FTIR) by light from inside the glass. What is FTIR? In total internal reflection, light stays inside the glass. However, light escapes wherever a material is within about a wavelength of the surface (thus, frustrated total internal reflection). That material can be marker ink, or as you see in the photo below, it can be the skin of my hand where it is pushed into close contact with the glass:

The glass is mounted on a steel or aluminum frame. Large sheets of glass (160 pounds, here) are dangerous to handle. Even tempered glass will shatter if struck on the edge. I preferred to have installation of the glass done by professional installers.

The glass is held to the frame by four standoffs, provided by the glass company. These are decorative, but each standoff contains a 3/8" bolt that passes through the frame, and through a 1/2 inch hole in the glass. The holes in the glass must be cut by the glass company before the glass is tempered. The standoff includes some nylon hardware that prevents the steel of the bolt from making direct contact with the glass, which could shatter it.

After the glass was mounted, I slipped an 8 foot strip of 80/20-brand aluminum extrusion over the upper and lower edges. The extrusion has a channel of width 10.19mm, which neatly slips onto the 10.0mm glass. It is held to the frame by simply sitting upon six-inch C-clamps. The glass is held to the frame by the standoffs above. The glass is not clamped to the frame. The clamps just support the aluminum extrusion.


Within each channel is an 8 foot strip of LEDs. I used a 5 meter 120 watt strip of white LEDs. In retrospect, a 48 watt strip would be bright enough and a lot cheaper. You will need one or two 5A 12V supplies, mounted on the frame. Heat sinking the 120W LED strip is important and the aluminum extrusion serves that purpose. I added an additional layer of electrical insulation between the extrusion and the LED strip, 1 mil Kapton tape 1/2 inch wide.


A 48W strip of LEDs shouldn't need heat sinking, so the extrusion would not be needed, nor the C-Clamps that the extrusion sits on.

Choices in markers


  • EXPO Neon dry-erase are easier to erase than other fluorescent markers, although not as easy to erase as ordinary dry-erase markers. Dried marker ink wipes off pretty well with dry paper towels. Wet marker ink smears, so I use glass cleaner only for the slight residue after wiping.

  • Liquid chalk Neon has one great advantage over dry-erase markers: it doesn't squeak. You have to pay more attention to keeping the tip saturated, in order to draw solid lines.