Tungsten light is redder. B/W panchromatic film is a bit less sensitive to red so the speed is reduced by about 1/3 stop.
Before the 1920s film was almost insensitive to red (orthochromatic). Pan was a great advance in the rendering of skin tones.
Thanks Mark. Yep, I remember panchromatic B/W film from the old days of photography (a few of my friends had their own labs at home) and the use of color filters to dramatically change the result. I prefer color film stock for motion pictures I am planning on. I do like fine grain B/W though - for example to make the (motion) film equivalent of fine art photography. Never found anything except test or unfinished footage though - and a Super 8mm film (shot on Canon double Super8 - surprisingly clean, sharp and steady) that won a Super 8mm short film contest way back in 1981, projected with a Bauer T 610. B/W also still pops up in music videos here and there. For some reason always in slow songs. Perhaps because it is more suitable to establish a certain mood (or period feel) and to focus on textures and lighting as opposed to fast moving subjects....