dimmer switch

plural dimmer switches

1. A light switch which can adjust the brightness of the switched lamp from dim to bright, as well as turning it on and off.

   Elder Price: "Well, Elder McKinley, I think it's okay that you're having gay thoughts just so long as you never act upon them." Elder McKinley: "No, because then you're just keeping it down, like a dimmer switch on low (on low), thinking nobody needs to know (Uh-oh!)"

   2011, Trey Parker, Robert Lopez, Matt Stone, “Turn It Off” (track 5), in The Book of Mormon: Original Broadway Cast Recording

2. rareA switch that changes the headlamps on a motor vehicle from low to high and from high to low beam; a high-beam switch; a brights switch.