Here is the skylight of Mathew Brady’s Washington studio. Today the space is occupied by the National Council of Negro Women. The studio itself today is nought but a storage room full of filing cabinets. But still being able to see the skylight Brady used to illuminate his subjects helps one imagine Abraham Lincoln and U.S. Grant sitting in that loft for the portraits we know them best by.
The skylight is on the top floor of the pink building at the left of the photo.
dcphotoartist 
The actual skylight still existed in the ceiling back in the 1970s. The skylight in the recent photo is not where the original was located. I have seen the original as my family once owned the building.