How to Create a Gradient Overlay in Photoshop
Many beginning Photoshop artists steer away from the gradient overlay because they don't understand how useful it can be. It can add cool effects to text, but you can also create a gradient overlay to control light sources and add highlights and shadows to selections.
Select the object you want to overlay. If it's part of a layer, copy it to its own layer (the "Command" and "J" keys). Make the new selection layer active and apply the "Gradient Overlay" layer style (in the Layers menu or from the Layers palette).
Check the preview button in the Layer Styles dialog so you can see your changes live. Your selection will fill with a black to white gradient but don't worry. With a few tweaks you will see dramatic results.
Change the blend mode to "Overlay" (try "Hard Light" for a more dramatic effect). The gradient will now mix softly into the layer's original colors.
Reset the angle to shift the light source. The white end of the gradient will be your highlights (reflected light) and the black will serve as your shadow areas (remember, you're not using the gradient overlay to cast shadows but to create the appearance of light being cast over the selection). Choose the "Linear" style to reflect a broad light source such as room light, and "Radial" to reflect a focused light source. Check "Reverse" to switch the gradient direction.
Click on the gradient preview to change the gradient colors. Click anywhere in the gradient bar to add a new color stop or click on a custom gradient to create a totally different effect.
Narrow the gradient focus with the scale slider. The lower the percentage the higher the mix of the right gradient color, the higher the percentage the more the left color will mix into the blend.
Tips & Warnings
- Use multiple color stops and the scale command to make the gradient reflect the highlights and shadows of the overall document. With a little tweaking you can make any layer copied from another document look like it's lit the same as the current image.