Step 1: For this Demonstration, you will need to create a new document... make the image size 78 pixels x 78 pixels.

Next make the background color any color of your choice (make it light)

Step 2: Set the Marquee tool to a Circle and make a Circle in the middle of your document. Next from the Options Tab of the Navigator Window, select Radial as the Type.

Finally Select the Gradient Tool and fill in the Circle using White and any other color, do this by clicking the top left part of the Circle and dragging all the way to the bottom right side.

Step 3: Ok, now from the Menu, click Select | Modify | Contract. Set the number to 5 and press OK. Now repeat Step 2 from within the new smaller circle and your Done!