Ooh...Linear Light..very interesting. You'll want to run through all of your blending modes (even I do it all the time) because each situation is different on how the light of two layers will 'play' with each other. We've got a mixture of different angles and directions but it makes it all the more complicated and intriguing...I should sell it at Sotheby's from a hi-res print...
Here is the document without the original layer set turned on (which I didn't show earlier).
To add an inner stroke to make a 'border/frame' if your background layer is locked. First have 'Thing' drag it to the new layer icon and then drag the locked layer to the oscar the grouch bin
and then you can add a Stroke it to the west effect.
Sweet sassy molassey. Bed of liquid ooey goo.
