This is one of over 4720 effects generated by Filter Forge, a Photoshop plugin that allows you to create your own filters.
To open this filter, you must have Filter Forge 1.0 or higher installed on your computer. If you don't have it installed yet, click here to download Filter Forge
A snippet for a new BlendMode that only affects the Luminance, Brightness or Y component of two images. You can either add, subtract or muliply them together,
blending blend mode add subtract multiply luminance brightness Y snippet