Does using brightness dimmer (screen filter) really save battery?

We know that the lower the scree light/brightness, the lower the battery consumption. There are some applications which provide ability (without root) to lower the brightness beyond the (default) limit. So, I want to know does it really save battery? In other words, does it affect battery consumption comparatively to default minimum limit? Btw, I'm also interested to know *how does such application do this task if going beyond limit?* And is there any command-tool related to settings brightness level?