Nice one OniyaMCD, the Arcane Lamp was perfect. A few dozen of these scattered around have the building lit perfectly. I'm not sure how the secondary light source thing works with them, but it does!Did a poke into Reddit, and someone mentioned Thaumcraft's 'Arcane Lamps', which apparently cover a pretty decent area. You may also consider 'floating' your lights (Nitor doesn't require a supporting block, only a block during placement, for example.) A 15 meter ceiling in a modern warehouse would likely have suspended fluorescent lights (sawing any light-producing block gives you a multitude of aesthetic choices).
(The irony is not lost, that in a high technology workshop, I had to resort to magic to light it.. lol)