To be more specific, dimming incandescent light bulbs (the old fashinined round ones that scorch your fingers when you unscrew them) will help a bit, but not as much as you'd think. That's because the ratio of wattage to lumen (energy to light output) is not 1:1. Incandescents are highly inefficient - with 80% of the wattage going to heat the light bulb rather than give off light - so when you dim one, you're not cutting the energy by nearly as much as you're cutting the light output. ( For example, if you dim it by 50%, you'll only be cutting wattage by about 30%.)
A better route: buy dimmable CFLs (the package needs to specifically state that they are dimmable, else they're not). Also be sure your dimmer is the newer model as the older resistor style can not accomodate CFLs. If you are not able to go that route but want low light, opt for as low a wattage incandescent as you can find. Better still - light a candle.