
This my interpretation of a tutorial I came across on the Internet. The process is very easy if you’re patient and follow the steps carefully. We will be using one of the coolest things in Photoshop: the super powerful Brush Engine.
First, open Adobe Photoshop and create a new document. I’m using 1920×1200.

Step 1: Creating the Bokeh brush
Select the Ellipse Tool (U) and create a circle. You can create a proportional circle if you go to Ellipse Options and select Proportional 1:1.

Use black for the color, and go to Layer → Layer Style → Blending Options. Change the Fill Opacity to 50%. Select Stroke and use 10 pixels for the size, Inside for the Position and Black for the color.

Go to Edit → Define Brush. Name it “Bokeh” and now we have a new brush! You can hide or delete the layer with the Ellipse because we only needed that shape to create the brush.

Now let’s define the brush. Go to Window → Brushes (F5). The first thing to do in the Brush Engine is to select our new Bokeh brush. The size won’t matter because you will change that when you use it. The Spacing, however, is very important. Change the value to 100%.

Select Shape Dynamics. Change the value of Size Jitter to 100% and Minimum Diameter to 50%.

Select Scattering. Change the value to 1000%. Also, increase the Count to 5 and lower the Count Jitter to 1%.

Select Other Dynamics. Change the values of Opacity Jitter and Flow Jitter to 50%.

Now that the Bokeh brush is ready, you will need to set the stage for your canvas.
Step 2: Creating the Canvas
Create a new layer and fill it with a very dark gray (#262626), not black. If you fill it with black the effect won’t work.

Go to Layer → Layer Style → Blending Options. Select Gradient Overlay. Change the Blend Mode to Overlay and Angle to 45º.

Change the gradient colors by clicking on the color box to open the Gradient Editor. The colors I used are: Yellow (#FFF799), Cyan (#1BDAEB), Purple (#9B3B81), and Orange (#D27E34).

Step 3: Paint!
Now that the stage is ready, we’re ready for the fun part, let’s paint! Create a new Folder in the Layer Palette. Rename the folder to Bokehs and change the Blend Mode to Color Dodge.

Create a new layer inside the Bokeh Folder. Choose white for the color and select the Brush Tool (B). Start painting some ellipses with our custom brush. For this first layer use a big size, like 500-600px.

Go to Filter → Blur → Gaussian Blur. For this first layer use 20 pixels for the Radius.

Create another layer and paint more brushes. This time use a smaller size for the brush, like 350-400px. Again blur the layer by going to Filter → Blur → Gaussian Blur. Use 4 pixels for the Radius.

Create another layer and repeat the previous step, this time use a much smaller brush, like 200-275px. Apply the Gaussian Blur to this layer as well, but use only 1 pixel for the Radius.

You can try different shapes for this effect, like hexagons or hearts for example. Play around with the blurs to add more depth to the final design. It’s entirely up to you! Have fun creating your digital bokeh wallpaper!
For more information about the Digital Bokeh Effect, check out Abduzeedo’s Tutorial.