The ring contains 36 LED's enclosed within a molded polyurethane encasement. It comes with 18 feet of lead wire to allow ample freedom of movement, especially when doing hand-held chroma key work. The plug-end is the Switchcraft mini XLR mate with the locking mechanism. This entire system was designed to be ultra-durable and very reliable under heavy use.

Green or Blue... which should I choose?

If you are shooting DV, green tends to carry a little more information and will probably be best for most applications, though blue is still very effective, especially if your subject is wearing something green!. I have read that, as a general rule, the blue chroma channel in DV footage can be inherently grainy and noisy, especially in low-light situations. However, tons and tons of video is shot every day using a blue screen, so it is certainly a viable color, depending on your format, amount of light, etc.

Mounting:

The rear of the LED ring has standard 72mm lens threads and will screw directly onto lenses with the same. If your lens threads are slightly larger or smaller than 72mm, a generic filter step-ring can be had for a few bucks via ebay, B&H or the local camera shop.

In the following two B&H links, you can select your camera lens thread size on the left:

Step Up Rings (if your lens threads are smaller than 72mm)
Step Down Rings (if your lens threads are larger than 72mm)