I've been asked to do a mapping projection onto a wall of an old church which is about 38m x 12m. My plan is to use two projectors. There will be some ambient lights but I don't think it'll be much so the projection are will be reasonably dark. I would like to know how much lumens do I really need to for each projector. Someone told me that 2 x 10,000 lumens projectors would be enough but I found some web site to calculate suggested lumens and according to this web site I would need at least 30,000 lumens each. The budget is limited so I need to know what lumens would be realistically "acceptable". I will really appreciate any suggestions and tips. Thanks a bunch in advance!