This is a rebuild of a previous lamp.
That lamp had things I either didn't like or didn't work too well:
1> Hairy-string - unattractive and liable to fail
2> Tape measure reel - non linear spring, also unattractive
3> Limited range (due to the spring above)
4> Untidy mains cable

To address these points I:
1 & 4> Replaced the string with PVC coated copper stranded wire
2 & 3> Replaced the spring with a counterweight

!Electrical!
This has not been electrically tested / appraised / approved, and I'm quite sure it would not meet UK / US standards for sale. No one is advised to reproduce this without being confident that they know what they're doing with mains electricity. Using a low voltage supply and LEDs would be a different matter.

Step 1: The Lamp Head

I bought an aluminium shade going cheap second-hand some months ago, because I thought it would come in useful for something.
I bought a ceiling fitting for a bayonet bulb, for something else but didn't use it.
I got some freecompact fluorescent bulbs as part of a local energy-saving scheme.
I have a lot of Lego:

The bayonet fitting pushes through half of a large grey vertical pivot, and through the shade, being secured with a threaded ring. A piece of Lego was added to the top to reduce the risk of touching the terminals with my fingers.

I fitted a 14W CF to this - it doesn't get very hot - higher wattage bulbs may not be suitable for this type of shade.

!Solder the ends of the mains wire right-up to the insulation, lamps should not be hung on loose strands!

Step 2: The Counterweighted Pulley System

The lamp head is hung from two lengths of wire each 1.7m (67") long. The weight of the lamp is counterbalanced by a weight (step) using pulleys such that the weight travels half the distance of the lamp.

Main parts:

The large wheel is needed to avoid excessive flex on the wires, it has good grooves for the purpose.
I used two ballast-weights for Lego boats ,and a collection of wheel-balancing weights I found (lead & zinc) Most of these were melted down and re-cast (future Instructable)

The main pulley is suspended from a roof beam by a screw, the wires are also attached to this mounting.

In the lower positions this is more like a desk-lamp for close-work, reading small-print etc. In the higher positions this is more like a ceiling lamp with wide coverage.

Step 3: Counterweight

This counterweight balances the lamp head.
It should be ~ twice the weight of the lamp.

Step 4: Main Pulley Block

This block bears the weight of the whole lamp and is screwed to a wooden roof-beam

Step 5: Assembly

The main pulley block was screwed to the beam, and the counterweight temporarily connected to it.
Then the wires were inserted, threaded around the pulleys and securely connected to the lamp head.
After being strung together the temporary connections were removed and the weighting adjusted.

Step 6: Power Supply

I hacked an old (non-functional) CF bulb for it's bayonet fitting. As I'm only running another similar bulb this is adequate for the purpose - a higher wattage device should not be connected to a light fitting in this way.

I also hacked an old electric-shaver cable, as the springy flexibility holds this nicely and is aesthetically more pleasing than straight cable.

Two holes were drilled in the CF fitting, and the cable pushed trough (a tight fit). The ends were soldered to the existing (red) wires and a quantity of car-body (styrene-based putty) used to fill and electrically insulate the device. To finish the job I squashed it onto a circle of wet filler and let it set, bit of sanding - done.

The curly lead was connected to the lamp with brass screw connectors from terminal-block

Step 7: Usage

Properly balanced this will run up and down very nicely with one hand.
In development I used nylon strimmer-line which was super-smooth, but I couldn't be happy with the electrical connection in that phase.