 Step 1 : First we need a background, I use this beautiful back-and-white photo, which has inspired me a lot:

Go to Image > Adjustments > Color Balance or press Ctrl-B to bring up the Color Balance box, adjust only Midtones settings to bring our photo a little color

 Step 2 : Reset your foreground and background colors by pressing D. Create a new layer and go to Filter > Render > Clouds to create some clouds

Go to Filter > Render > Difference Clouds and repeat this effect some times (by pressing Ctrl- F) until you get an image like this Notice that we should have some white clouds on the left because they will transfer into light in a next few steps

 Step 3 : Go to Image > Adjustments > Brightness / Contrast and use the following settings:

Increase the black and white areas by going to Image > Adjustments > Levels (Ctrl-L), move the black and white points to the center

 Step 4 : Go to Filter > Blur > Motion Blur and use these settings:

Change the blending mode of this layer to Soft Light

If the light is still too sharp, go to Filter > Blur > Gaussian Blur, adjust it to make the light blur enough

 Step 5 : In this step, we will make the light more realistic. Create a vector mask on the current layer (by pressing the Add vector mask at the bottom of Layers tab) and use the Gradient tool with White to Black and Radial Gradient options to draw a line from the top- right to the bottom-left corner

Now our light had the gradient effect! Press Ctrl-J to duplicate this layer, our light will become brighter.

 Step 6 : Bring a little color to our light! We can't apply color directly to the white light we has created with Hue/Saturation or Color Balance so we will use a little trick here. Create a new layer and use the Brush tool with a soft brush and orange foreground (#ffa800). Now paint your photo like this:

Change the Blending mode to Soft Light