CD stack lamp

CD lamp by Chad Johnston

I’ve been eye-balling CD stack lamps such as this, this and this for ages, naturally with the intent of making one myself. I actually even started working on one several years ago (2006 or so), but kinda forgot about it shortly afterwards as the lamp solution turned out relatively inefficient. Back then, my plan was to use recycled CCFLs (stripped from old TFT displays). With these, it quickly became apparent that the energy consumption (around 15W) wasn’t really up to par with the amount of light created. Sure enough, lamp projects such as this should be considered mainly for decorative purposes with little emphasis given to functional lighting. But still, getting a bit more than a dim glow would be nice. After all, the CD stack dims down the light source to some extent.

Ok so after the initial build sessions, the project has been on hold right about until a month ago. That’s when I came across these relatively cheap white LED strips and decided to buy one for test use. A 20€ “starter pack” included a 1-meter-long flexible rubber insulated LED strip, some plastic mounting clips and a +12VDC wall-wart. The LED strip has also a adhesive surface (double-sided tape) on the reverse side, so besides using the supplied clips it can also be glued to a smooth surface. There’s also a extension connector allowing multiple strips to be chained, but for this use the bundled wall-wart is under-powered.. Drop in a second strip, and you’re already over 50mA past the wall-wart spec!

As for light intensity, this single LED strip is waaayy better than the CCFLs. By sight, I’d estimate the LEDs being at least twice as much intense. As this is obtained with about one third the power consumption (below 5W), the strip is just about perfect for decorative lighting.

Fiddling around a bit more with the LEDs, it soon became apparent that the adhesive on the reverse side is absolute shit. In no time it was peeling off here and there, so better remove it altogether then! If was to use this method of affixing the strip somewhere, I’d definitely replace the readily-installed adhesive with some decent double-sided tape.

Inside the rubbery insulation, the LEDs are chained in pairs of three along with a appropriate series resistor. Between these pairs is a cutting point with soldering pads, allowing for length adjustments. Of course, the rubbery insulation needs to be removed in order to solder wires to them, but nonetheless this is still about as handy a way for fine tuning the length as it gets.

One of the cutting points on the LED strip.

I figured that dividing the strip to four equal length pieces would be enough to distribute the light “a full circle”, so I cut the strip in half and connected the halves parallel to the wall-wart connector. On the top, the strip halves are simply bent over a 8mm threaded rod. The latter will also double as support structure, keeping the stack of CDs in place with the lamp base.

LED strip cut to half and halves connected parallel.

As for the lamp base, I decided to do a two-part structure. The upper part has a small slot for centering the CD stack with the threaded rod and pass-through holes for cabling, whereas the lower part has a wide recess for affixing the rod and the upper part. The base plates could’ve been combined to a single part, but I figured maybe I’ll take it easy with the CAD practice. Material-wise, the base plates are leftovers from my rack trolley project (read: pine).

Upper sides of base plates.

Lower sides of base plates

In case you’re wondering about the pockets on the upper part, they don’t really have any functional purpose for the lamp itself. They’re there just because I wanted to practice using basic CAD tools (like fillet/chamfer) :). Anyway, once I had the base plates, there wasn’t really much more to it..

Base plates and LED strip assembled with the 8mm shaft.

For assembling the stacks of CDs, I used clear silicone to glue the discs together. Silicone is slow to dry, leaving ample time for aligning the discs. Once it dries up though, it becomes pretty rigid; the stack I have can withstand being held at any angle from either end without breaking apart. The complete stack was done in phases; first by making several small stacks and then, once the silicone had dried up, by combining these together. For the latter, I clamped the entire stack to the kitchen desk. Approved by the missus, of course ;)

The full stack of discs drying up, clamped to the kitchen table :)

The center holes needed to be enlarged to 20mm diameter. I didn’t even come to think of this part until I had the stack assembled, but lucky for me there was one enlarging drill bit (that also had a lengthy shaft) at the workshop. Had I done the enlarging prior to glueing, a conventional length enlarging drill bit would’ve been just fine. Oh well, next time then!

Which one you see, yours truly minus a head or the enlarged center hole? =)

One other thing I didn’t come to think of at all was that most CDs are usually slightly thicker from the middle. Hence, if you glue multiple discs together with the intent of having no gaps in-between, the discs will bend. With my method of stack assembly, this means that you’ll end up with bigger gaps here and there. Using less pressure while glueing would’ve allowed for a more evenly divided gap spacing.. Sounds like one more for the “next time”.

Gaps between the discs..

From the angle above, pan back a bit and..

Let there be hous.. err.. light!

Ta-daah?

What remains to be done is treating the base with some varnish or paint (need a matching color, halp!). One further option would be to divide/rewire the LED strips from the top as well. This would allow taking the threaded rod above the top of the CD stack, in turn allowing for some kind of a locking nut/cap. This would make the entire structure solid, fastening the CD stack to the base.. Though judging by the weight and overall structure of the lamp, I find it very unlikely that it’s going to tip over easily..

Now go check out 22 ways to recycle old CDs @ Interbent :)