Create Visible Light

1. Load up your start images. I'm using a naff looking light, a naff looking wood grain texture and an even naffer looking wall. (This could also be an exercise in making a silk purse out of a sow's ear)

2. First thing is to make a new layer above the lamp and throw some shadow on it. Use a large, soft edged brush with the opacity set to about 15. Leave the area beneath the lampshade clear but put some shadow along the desk top. Build the shadow's up gradually so as not to leave any definite edge's -

3. Make a new layer above the shadow layer. Select your Pen Tool and make a selection along the bottom edge of the lampshade.
TIP: It is much easier to see what you're doing with the Pen Tool if you have the
Rubber Band option selected -

Once you have the bottom edge selected carry on and extend the selection until
you have something like this -

4. Now convert the path to a selection (Right click with the pen tool and choose Make Selection) and hit QuickMask (it's the shaded rectangle with the circle in the center near the bottom of the Toolbar)

5. We are going to blur the edges of the selection with the help of the QuickMask. Go to Filter>Blur>Gaussian Blur and enter a value of around 5px. Hit OK.
6. Come out of QuickMask Mode (hit the button to the left of the QuickMask button), you will
be left with the ‘marching ants’ around the selected area -

7. To make the light rays we are going to use the Gradient Tool set to 'Foreground TO Transparent' with a light yellow selected as the Foreground Colour.

8. Apply the gradient starting about half way up the lampshade and finish about half way down the selected area. You should have something like this -

DO NOT DE-SELECT JUST YET.
9. Take a soft edged, round brush and paint in a bit of white just underneath the lampshade -

10. De-select.
11. Because we applied blur to the selection there is a bit of over-spill round the edge of the lampshade that needs to be removed. To make the lampshade easier to see, turn off the light ray’s layer.

12. Make a selection (Pen Tool) along the bottom edge of the lampshade as before, but this time extend it upwards. About half way up the shade and back to the start point. Convert this to a selection, turn on and select the light rays layer and hit backspace. This will clean up the bottom edge of the lampshade -

13. Now to make a pool of light on the desk. Use the Elliptical Marquee Tool to make an oval selection on the desk -

14. Now go to Select>Feather (or Ctrl+Alt+D) and enter a value of around 10px. Select the shadow layer and hit backspace. De-Select (Ctrl+D) -

That is basically it. You may want to adjust the opacity of the light ray’s layer to make it look more natural or even use the Colour Dodge Tool to add some lighter areas to the light pool. Just experiment, that’s what it’s all about.