If you can contact a studio lighting supplier they can supply a red gel that goes over studio lights. Only needs one layer (cellophane will need a few). Alternatively any automotive nic nak shop (you know the one that have everything your car needs but you never realized was essential) has red lens paint (like nail polish) for repainting the glass/plastic stop lens of you car. Just keep adding layers until its dark enough. Make sure you wait for it to dry properly between layers otherwise it wrinkles. Not that that makes much of a difference on a lantern when you're 200 km from civilization. Appearances are everything of course.
