I bought an inexpensive fluorescent desk lamp to install above a desk. I wanted it to not show any wires and to look as clean as possible. This instructable shows how I went about doing this easily. You may find it useful if you are in the same predicament to see how I solved the problem. Please note: Your lamp fixture may vary, so this is only a guideline on what to do.
Please watch the video as you view through the instructable as it shows very clearly what was done. An external link to the video is also shown here: Easy Hidden Wire Fluorescent Lamp Installation
First Thing... Open The Fixture
Remove the cover from the fluorescent bulb and remove the bulb and place them somewhere on a safe and soft surface so you don't accidentally break anything or have it roll off the table and smash on the ground. Using a screw-driver, you can pry open the cover for the electronics in the lamp, as you can see by the photos. You will need access to the wiring inside.
Step 1: Cutting the Cord
The lamp I bought had a cable on it with a large plug. It was also coming out the side of the lamp (which would be visible). I wanted it to come out the back so it would be hidden. So the first thing I had to do was cut the cord as it entered the lamp. This will allow you to thread the end of the cord through smaller holes since otherwise you would have to make a huge hole to fit the plug through. You could also de-solder the cord or your lamp may have it attached at a junction point with some screws or clips.
In my case, the easiest thing to do was cut and then rejoin the cord with Marettes (otherwise known as "twist-on-wire-connectors" or those orange things in the photos). I made sure I marked the cord before cutting so I would connect the wires back the same way. It shouldn't matter but better safe than sorry, as some lamps and/or plugs may be polarized.
One more thing... At this point, if your cord is not long enough to reach your outlet socket, you can wire in an extension cord directly. Just replace the cut end with your plug, for another longer cord with a plug. Just be sure you are using the same wire-rating (gauge), following the polarity and grounding if necessary.
I had to drill a small hole through the back of the lamp fixture casing (which is plastic) to let the cable through from the back of the desk and into the lamp. If you have a hole there already, you can perhaps use that. I had a hole on the back of the case already made for the screws that attach the fixture, but I preferred to make my own as the location is better. So using a drill bit, make a hole that is slightly larger than the cord so you can pass it through easily but snug.
Step 2: Drill and Thread
Drilling Your Furniture
Carefully measure and cut a hole in the back of your desk where it will line up exactly with the lamp fixture. You can even place the fixture and use a pen to mark the hole and verify, just in case you don't trust your measurements. You know what they say.... "Measure twice, cut once!"
Threading the Cord
Now that you have a hole in your furniture, and a hole in your light fixture, it is time to thread the cord through. Start with the end you cut near the lamp (opposite the plug) and pass it through the back of your desk, through the hole and to the front. Then pass it from the outside of the hole in your lamp to the inside.
Once inside, you will join the ends of the cord with Marettes (those orange "twist-on wire-connectors" in the photos) to the other end of the cord which you cut, so that everything is wired back up the way it started. Before you close anything up, you can now plug in your cord and test that your lamp works. Be careful as there will be live wires exposed and you could get shocked. If you are not sure, don't plug anything in and do it when things are closed to be safer.
You will also notice that the cord originally was tied underneath two plastic clips in the lightning fixture. This is to prevent the cord from pulling on the electrical connections. So you will notice in the last photo I pushed the cord back under to keep it from sliding and putting tension on the Marettes.
Step 3: Last Few Screws
Positioning The Lamp
At this point, you can pull your cord tightly back and "tow" your light fixture up into place. It will be held up on one side by the cord, and you can tape up the other side temporarily (or ask a friend to help) to hold the fixture up while you drill holes for your final mounting screws.
You will notice the holes are shaped like little key-holes. The larger part allows you to slip it over a screw head, and then you slide the fixture sideways so that the screw slides into the narrower part. Then you tighten the screw. But because of the modifications we made, since the cord is coming out the back it is at 90-degrees to the sliding path, there is no room for lateral movement of your lamp. Since I don't care about this "slide and release" feature for the keyhole screws, simply screw the fixture into place by placing screws directly through the narrower part of the keyhole.
Since I am using hard wood, I couldn't self-tap the screws in. Also, if you are mounting into Ikea-style furniture made of "particle-board" or "chip-board", you will also need to pre-drill. So using a smaller drill bit than the screw, make some smaller "pilot holes" in the wood through the narrow part of the light fixture. You can see in the video and photos how I drill the holes, then use a screw-driver to place the final screws and drive the fixture to it's final resting place. Once in place, you can remove the tape that you used to help hold the light fixture in place (or your friend's fingers).
Step 4: Final Result
Relax and Enjoy
Now just place back your fluorescent bulb and cover on the light fixture. Plug in your lamp and turn it on, and pat yourself on the back for a job well done!