To answer anyone looking at this now: the Rayleigh scattering needs to produce diffuse light [0]. Which actually makes the project easier to pull off since you just need to place secondary lights all around the roof and walls of the room that emit AM1.5 diffuse light globally and not worry about any sort of filtering on the main light, which you need to match to AM1.5 direct.

[0] Applied Photovoltaics, Earthscan Publications, 2007: http://www.eng.uc.edu/~beaucag/Classes/SolarPowerForAfrica/B...