The idea for this Instructable came from something I found called Sun and Moon Jars on ThinkGeek.com.

http://www.thinkgeek.com/homeoffice/lights/994a/

Unfortunately these jars cost much more than I was willing to spend. Because of this, I decided to make my own version, and share it with all of you.

Step 1: What You'll Need

Tools and Materials
~Screwdriver
~Some form of glue
~Soldering Iron (You may not need this)
~Dremel or similar tool.
~Solar-powered garden light
~Glass Jar
~Frosted Glass Finish Spray (You may not need this if your jar is already frosted)
~Paint for use on metal (Optional)
~Safety Glasses

Before you get started. Make sure you know what you're doing, and observe all safety procedures. That means you should probably wear safety glasses and any other appropriate safety attire. Otherwise, you might end up with a piece of plastic or metal in your eye. Trust me, it's not fun.

Step 2: Disassembly

First, you'll have to take apart your garden light. This process will be slightly different for all lights, so I won't go in to great detail here.
Basically, remove the post and stake until you get to just the head with the LED and Solar Cell.

Then, you'll have to remove any screws you encounter until you can get to the internal circuitry with the battery and LED.

Step 3: The LED

Unless you want a white glowing jar, you'll either want to replace or modify the current LED that came built into your garden light.

Replacement:
If you chose to replace the LED, make sure the LED you're using has the same voltage ratings as the one built into the garden light .The LED in my light ran off only a single rechargeable "AA" battery, (1.2v)

Modification:
In this case, the term "modification" is simply a fancy term for "color."
So if you chose to color your LED, choose a suitable Sharpie or other permanent marker, and color away. Try to color the entire LED, leaving no clear space.

Step 4: Make It Fit

Your light probably won't fit in the jar as it is, so you'll have to trim it down to size.
I used a dremel with a cutting wheel to cut away a lot of the plastic until I could make the solar light fit into the jar,
Feel free to use any methods you feel appropriate to cut it down to size.
Just remember, safety first.

Step 5: The Jar Lid

Now, in order for sunlight to get to the solar cell, you'll have to make a hole in the jar's lid.

Measure or trace the solar cell on the lid.
Then, cut out a square of the lid so your solar cell can shine through the top. (or rather, so the sun can shine through onto the solar cell)

If your garden light uses a CdS photoresistor to measure the amount of light reaching it, you'll have to cut or drill another hole for that.

Step 6: Painting the Jar Lid

You may wish to paint the lid. Now is the time for that.
Paint it any color you'd like. I chose a metallic silver.
After you've painted it, you'll probably want to seal it with a clear sealer.

Step 7: Solar Cell Lid

Now, it's time to attach your solar cell, battery, and LED to the lid.

Align your solar cell with the opening of the lid, and attach it using any glue you'd like. I would recommend either hot glue or Gorilla Glue. Try to seal it as best you can so no pesky raindrops can leak through.

Step 8: Jar Frosting

In order for your jar to glow, rather than just shine a dim light through it, you'll have to frost the glass.
To do this, you'll need to give it a coat or two of a translucent frosted finish spray paint. It may also be possible to do this with a very thin coat of white paint, but it's probably best to stick with the frosted finish spray.