Compound shadows

I have a scene with a light bar with a relatively large number of light sources in it. I have data I am using to look up illumination for the entire light bar taken from real world data. Ideally this light bar would produce compound shadows. I don’t think rendering a separate depth pass for each individual light is going to be practical (could in 100’s). The depth complexity of what is being illuminated is relatively simple. Does any one have/ or know of any techniques for approximating the compound shadows you would get from an array of relatively tightly packed light sources. The shadows do not have to be super accurate, but it does have to run in real-time. I imagine I am not the first person who has run into this, especially with the increased usage of LED lighting.

Take look at this :