First off: What kind of film are you shooting? 16mm? 35mm?
Second: Whenever you're shooting on film -NOT video- you ALWAYS need a light meter, and you must know how to properly get readings.
If you're shooting on video, it's still a good idea to have a light meter so that you can attain consistency in your images.
Your question of whether or not you need a light meter whilst shooting film- I can guarantee you that you will end up nowhere near your intended look and feel of your scenes. Shooting noir-style entails many different variables; not just cinematography alone, but production design, wardrobe (for specific color densities), processing, color timing techniques, and many others.
If this is an exercise and not for a client, you don't have a lot to worry about as no one except yourself will care about the finished product and it will be a good learning experience for you; still- GET A LIGHT METER. Rent one if you have to.
Once you get the meter, set it to the ASA or ISO of your film (video is widely accepted as 400 ASA). Then, set your aperture to 2.8 and try to get the key side of your actor's faces to come in at 80 foot candles. Everything else in the frame that is not directly related to the story (meaning it should be secondary in terms of importance to the audience) should come in at a minimum 1/2 stop under your fill light. Find out what the latitude of your film is so you can control your contrast.
If you can't get your light sources bright (inside) or dark (outside) enough, change your master scene aperture setting to a point where you have one or two stops light in either direction.
Good luck.
