First, choose your image and import it into Photoshop. Now, duplicate your image.
Now you want to make a selection of your subject. This selection does not need to be perfect (especially on the side away from the background light). As long as youi are fairly close to the edges you will be fine. Of course the more accurate you are the better your results will be
Hopefully, you can see my selection here. The next step is to create a mask on your copy layer. This will separate your subject from the background.
Now you need to add a layer between your background and your copy layer. This is where you will be adding your background light.
Once you have done that you will need to fill this layer with a color. What I usually do is take my eyedropper tool and sample the background (on the background layer) close to the subject’s head on the side you will be placing the light. Then I open up my color palette and move the color to a lighter shade (usually halfway between where it is now and white). Now go ahead and fill this layer with that color. The next step is where you refine your background light. Choose the gradient tool and select “Radial Gradient”. Make sure your gradient is set Black to White. Pull a line from where you want the light to start out to where it will end.
At this point, you can see that I have refined the light even more. I erased the light on the left side and used a curves adjustment to lighten the light even more (that is up to your taste).
Here is the result
Not only does it save you from buying a dedicated background light, but I would say the result is much better then if you HAD used a background light. This truly only take no more than 5 minutes to do.
Ps: you can also move the light around on that extra layer.
I hope you have enjoyed this tutorial and will give it a try