Let there be light!
Creating simple lighting effects is not only easy, but fun and rewarding for as much minimal effort it takes in Photoshop:
Start with an image of a lamp, flashlight, torch, or whatever emits a beam of light.
Create a new layer. Now, using the Polygonal Lasso Tool, draw the shape your light beam will be. In this case I used the edge of the lamp head to determine the shape.
Now select the Elliptical Marquee Tool. This will create the oval end of our beam of light as it rests on the desk. To add this to the beam, hold down the shift button and drag out to create a nice rounded end to your beam.
Select the Gradient Tool, make the foreground color white, or whatever color you want the light to be, and set the options to Foreground to Transparent. Then click and drag the gradient line in the direction of the beam from the light source down to the table surface.
Now create another new layer and drag it between your background and the light beam. Using the Elliptical Marquee Tool, drag an ellipse that fits in the circular end of the light beam and fill it with white.
Now click Filter > Blur > Gaussian Glur and set the lever really low, like .3 - .5. Just enough to give the outer edges a little softness.
That's it! This is just the beginning. Once you have the grasp of this useful technique, there's no end to how many ways you can use it.