This tutorial explains how to create a shiny plastic look.
This is a pretty hard tutorial to go through for the first time. Once you've succeeded, you will be able to create some nice shades for any shape, not just circles.
Create a new layer. Make a round selection using the Elliptical Marquee¹ tool. Fill it with a middle-shade color (not very dark, somthing like R: 0; G: 178; B: 235; HEX: 00B2EB;) unsing the Paint Bucket¹ tool.
Expand selection (Select > Modify > Expand) by a value of 5.
Using the Rectangular Marquee¹ tool shift the selection top and left 8 pixels.
Use the arrow keys for precise movement.
Subtract selection² of the blue circle from the current active selection.
Feather the selection by a value of 10 (Select > Feather). Move the resulting selection back into the circle.
This is a very important step where you have to define the selection for your future light. You might want to repeat it a couple of times depending on the result you will get in the future steps.
Create a new layer, group² it with the circle layer. All other layers should be grouped with it as well. Fill the selection with black using the Paint Bucket¹. Set Blending Mode to Color Burn.
Crea
te a new layer and fill the selection with white using the Paint Bucket¹ tool.
This will create a ve
ry nice ambient light. It's hardly noticable but it will make your light look white and not "blueish".
Duplicate the layer created in the previous step. Set Blending Mode to Color Dodge. Adjust Opacity of the layer (50-60%) to the point where the light reflection looks just right.
Make a copy of the last three layer created. Link all three copies and rotate them 180° (Edit > Transfer > Rotate 180°). Offset them to the bottom right side of the blue circle.
Reduce the brightness of the bottom right side by adjusting Opacity (30-40%) of the layer which has Color Dodge mode.
Apply the Inner Glow layer effect (Layer > Effects > Inner Glow) with the color set to R: 0; G: 113; B: 149; HEX: 007195; and other settings set to the values shown in the picture.
Apply the Drop Shadow layer effect (Layer > Effects > Drop Shadow). Set all the values as shown in the picture.
And here it is! This is what you should have at this point. If you are unhappy with the look of the lighting look like, try to set the different Feather Radius in the step 5 or different distance in the step 4.