I've started the process of building a desk lamp using an array of white LEDs attached to a printed circuit board. This is based on a design by Ingo Maurer. Here's a picture of the Maurer lamp.
Here is the schematic for the first 9 strings of LEDs and resistors:
In reality, however, there will be 168 strings, for a total of 504 LEDs. Notice that these 9 strings only draw 187.1 mA. This means that the entire lamp will probably draw about 3.5 Amps at it's brightest, and it will be extremely bright. The lamp will be powered by a simple ~ 4Amp 12-volt power supply with a variable current limiter using a MOSFET and variable resistor.
Here's the board layout of a smaller version with only 26 strings:
As this circuit board isn't an "off-the-shelf" item, I'm having the good folks at ExpressPCB etch one to my specifications. They have a great process where one can use their software to "build" your schematic and board, and then send it to them electronically. They then etch it and ship it overnight. You can have a custom board delivered to your door within a few days (or faster, if you're willing to pay to expedite the service). Pretty neat.
The board will be held above the desk by a small vice-grip pliers, welded to a steel rod. At its other end, the rod will be welded to a 2" diameter solid metal ball, held in place by a large metal bushing welded to a steel plate. I've not yet completed designing the armature apparatus. Because it's relatively low voltage, I've decided to leave the circuit board completely exposed - It's cooler looking that way. Although, I may coat it with a few layers of varnish to afford some protection against accidental spills.