Lighting is an important part of any production but it can be critical for a horror or suspense movie.  A hinted or implied impression of something that’s there can be more powerful than seeing it in full.  It causes the audience to use their imagination and the fear of the unknown can be terrifying.  If you are making a low budget film then shadows are your friend.  They can hide mistakes, unfinished areas of a set, change the mood of a scene and much more.  Instead of showing the actual monster you can show the shadow instead.  This implies that something sinister is there, but just out of reach, and creates tension.  It also gives the audience something to look at but could be something as simple as a life-size cardboard cutout in the shape of the monster.

Some examples that could easily be used in a production:

• If you have a flying saucer, you don’t need to actually show it at all.  Instead you can show the actors being overtaken by a large shadow from overhead.
• Glowing eyes in the darkness, this could even be used to produce a chase scene by having the eyes appear in various places while the actor is running away.  Combined with sound effects and proper background music a scene with tension a lot of tension can be created without ever showing what’s lurking in the shadows.
• A hand reaching out from the shadows.
• A flash of the shadow on the walls near the actor.
• A glimpse of eyes staring out from the darkness, highlighted by a streak of light to make them stand out.  This effect is used very effectively in things like vampire movies and is one way to let viewers know that character may have dubious motives.

So it’s important to be sure you are effectively using the appropriate lighting technique to set the mood for your scene.  Granted, a professional lighting setup can be very expensive but it doesn’t have to be.  You can use any kind of light source as long as it looks good on screen.  If you are drawing a blank as to how shadows can set a mood, try watching some old film noir movies.  They masterfully create tension and suspense in a scene by having a strong contrast between the light and the dark, as well as casting large portions of the set and parts of the actors in heavy shadow.