ADDING GAMMA/NORMAL TO BRIDGE MODEL (gives bridge darkening effect at red alert)
Just before export nif in Max3: create two dummy helpers, name one Normal, the other Gamma. Select all parts of bridge you want to make dark (I usually select everything except maybe light and lcars). Click on the Link button in menu (looks like a magnet). You can then either select Normal from drop-down menu, or drag the selected parts to the Normal dummy (you'll see stretchy lines converging on dummy) and release when it higlights. Then click (or menu select) Normal dummy and repeat same process linking it to the Gamma dummy. You can test you have right result by going into Edit/ Select By Name and in Select Objects box menu ticking display subtree. You should see a hierarchy then with Gamma at top, then Normal and bridge parts you selected under Normal. You can export nif ok with helpers un-hidden but I usually hide them first. If you get weird seat/liftdoors flipping off effect ingame (I got that on a few bridges), just unlink from Normal. It means they won't darken but not end of world.
(edited to clarify)
