It's certainly not the sexiest piece of gear you're going to deal with, but dimmer switches can be unbelievably handy, especially if you have limited time and a limited budget, and you're already working with DIY lights. A dimmer switch, if you're not sure, is exactly what it sounds like: it's a way to selectively dim or brighten the quantity of a light source using electricity, rather than manual means like placing a net over the light. This is an important distinction as you're not trying to change the shape or quality of the light -- just simply lower the output. Most of these can be built for very little cost, so click through to check out some tutorials on building your very own dimmer switches.
Here is Film Force's tutorial for a dimmer switch:
Check out Film Riot's tutorial with a DIY China ball and dimmer switch (with some other bits after -- the video is a bit old):
Here is a dimmer tutorial from the The Frugal Filmmaker:
While it may look easy, it's also definitely easy to screw up if you're not paying careful attention -- and there is a risk of electrocution (as with anything electrical). It's also important that you get the correct gauge wire for the amount of electricity you're planning on putting through the dimmer. These can be a fire hazard if used improperly, so it's important that you know what kind of wattage you're shooting for before you actually build the light.
As was mentioned above, these work best with incandescent lights, as you can run into flicker issues with other light sources. Of course, these aren't just useful for filmmaking, as you can plug them into any lamp when they're not being used on your film set.
What do you guys think? For those who have built your own dimmer switches, what was your process like? Which style do you prefer?